Added some exercises
This commit is contained in:
Nicolas P. Rougier
parent
26f1f77460
commit
03ccfbdd33
159
README.html
159
README.html
@ -4,12 +4,12 @@
|
||||
<head>
|
||||
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
||||
<meta name="generator" content="Docutils 0.12: http://docutils.sourceforge.net/" />
|
||||
<title>100 numpy exercises</title>
|
||||
<title>100 numpy exercises</title>
|
||||
<link rel="stylesheet" href="numpy.css" type="text/css" />
|
||||
</head>
|
||||
<body>
|
||||
<div class="document" id="numpy-exercises">
|
||||
<h1 class="title">100 numpy exercises</h1>
|
||||
<h1 class="title">100 numpy exercises</h1>
|
||||
<h2 class="subtitle" id="a-joint-effort-of-the-numpy-community">A joint effort of the numpy community</h2>
|
||||
|
||||
<p>The goal is both to offer a quick reference for new and old users and to
|
||||
@ -48,7 +48,7 @@ is:</p>
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">Z</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">How to get the documentation of the numpy add function from the command line ? (★☆☆)</p>
|
||||
<li><p class="first">How to get the documentation of the numpy add function from the command line? (★☆☆)</p>
|
||||
<pre class="code bash literal-block">
|
||||
python -c <span class="literal string double">"import numpy; numpy.info(numpy.add)"</span>
|
||||
</pre>
|
||||
@ -116,7 +116,7 @@ python -c <span class="literal string double">"import numpy; numpy.info(num
|
||||
<span class="name">Z</span><span class="punctuation">[</span><span class="literal number integer">1</span><span class="punctuation">:</span><span class="operator">-</span><span class="literal number integer">1</span><span class="punctuation">,</span><span class="literal number integer">1</span><span class="punctuation">:</span><span class="operator">-</span><span class="literal number integer">1</span><span class="punctuation">]</span> <span class="operator">=</span> <span class="literal number integer">0</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">What is the result of the following expression ? (★☆☆)</p>
|
||||
<li><p class="first">What is the result of the following expression? (★☆☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="literal number integer">0</span> <span class="operator">*</span> <span class="name">np</span><span class="operator">.</span><span class="name">nan</span>
|
||||
<span class="name">np</span><span class="operator">.</span><span class="name">nan</span> <span class="operator">==</span> <span class="name">np</span><span class="operator">.</span><span class="name">nan</span>
|
||||
@ -139,7 +139,7 @@ python -c <span class="literal string double">"import numpy; numpy.info(num
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">Z</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element ?</p>
|
||||
<li><p class="first">Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element?</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">np</span><span class="operator">.</span><span class="name">unravel_index</span><span class="punctuation">(</span><span class="literal number integer">100</span><span class="punctuation">,(</span><span class="literal number integer">6</span><span class="punctuation">,</span><span class="literal number integer">7</span><span class="punctuation">,</span><span class="literal number integer">8</span><span class="punctuation">)))</span>
|
||||
</pre>
|
||||
@ -158,13 +158,21 @@ python -c <span class="literal string double">"import numpy; numpy.info(num
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">Z</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Create a custom dtype that describes a color as four unisgned bytes (RGBA) (★☆☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="name">color</span> <span class="operator">=</span> <span class="name">np</span><span class="operator">.</span><span class="name">dtype</span><span class="punctuation">([(</span><span class="literal string double">"r"</span><span class="punctuation">,</span> <span class="name">np</span><span class="operator">.</span><span class="name">ubyte</span><span class="punctuation">,</span> <span class="literal number integer">1</span><span class="punctuation">),</span>
|
||||
<span class="punctuation">(</span><span class="literal string double">"g"</span><span class="punctuation">,</span> <span class="name">np</span><span class="operator">.</span><span class="name">ubyte</span><span class="punctuation">,</span> <span class="literal number integer">1</span><span class="punctuation">),</span>
|
||||
<span class="punctuation">(</span><span class="literal string double">"b"</span><span class="punctuation">,</span> <span class="name">np</span><span class="operator">.</span><span class="name">ubyte</span><span class="punctuation">,</span> <span class="literal number integer">1</span><span class="punctuation">),</span>
|
||||
<span class="punctuation">(</span><span class="literal string double">"a"</span><span class="punctuation">,</span> <span class="name">np</span><span class="operator">.</span><span class="name">ubyte</span><span class="punctuation">,</span> <span class="literal number integer">1</span><span class="punctuation">)])</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Multiply a 5x3 matrix by a 3x2 matrix (real matrix product) (★☆☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="name">Z</span> <span class="operator">=</span> <span class="name">np</span><span class="operator">.</span><span class="name">dot</span><span class="punctuation">(</span><span class="name">np</span><span class="operator">.</span><span class="name">ones</span><span class="punctuation">((</span><span class="literal number integer">5</span><span class="punctuation">,</span><span class="literal number integer">3</span><span class="punctuation">)),</span> <span class="name">np</span><span class="operator">.</span><span class="name">ones</span><span class="punctuation">((</span><span class="literal number integer">3</span><span class="punctuation">,</span><span class="literal number integer">2</span><span class="punctuation">)))</span>
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">Z</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Given a 1D array, negate all elements which are between 3 and 8, in place. (★☆☆)</p>
|
||||
<li><p class="first">Given a 1D array, negate all elements which are between 3 and 8, in place. (★☆☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Evgeni Burovski</span>
|
||||
|
||||
@ -172,6 +180,53 @@ python -c <span class="literal string double">"import numpy; numpy.info(num
|
||||
<span class="name">Z</span><span class="punctuation">[(</span><span class="literal number integer">3</span> <span class="operator"><</span> <span class="name">Z</span><span class="punctuation">)</span> <span class="operator">&</span> <span class="punctuation">(</span><span class="name">Z</span> <span class="operator"><=</span> <span class="literal number integer">8</span><span class="punctuation">)]</span> <span class="operator">*=</span> <span class="operator">-</span><span class="literal number integer">1</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">What is the output of the following script? (★☆☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Jake VanderPlas</span>
|
||||
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name builtin">sum</span><span class="punctuation">(</span><span class="name builtin">range</span><span class="punctuation">(</span><span class="literal number integer">5</span><span class="punctuation">),</span><span class="operator">-</span><span class="literal number integer">1</span><span class="punctuation">))</span>
|
||||
<span class="keyword namespace">from</span> <span class="name namespace">numpy</span> <span class="keyword namespace">import</span> <span class="operator">*</span>
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name builtin">sum</span><span class="punctuation">(</span><span class="name builtin">range</span><span class="punctuation">(</span><span class="literal number integer">5</span><span class="punctuation">),</span><span class="operator">-</span><span class="literal number integer">1</span><span class="punctuation">))</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Consider an integer vector Z, which of these expressions are legal? (★☆☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="name">Z</span><span class="operator">**</span><span class="name">Z</span>
|
||||
<span class="literal number integer">2</span> <span class="operator"><<</span> <span class="name">Z</span> <span class="operator">>></span> <span class="literal number integer">2</span>
|
||||
<span class="name">Z</span> <span class="operator"><-</span> <span class="name">Z</span>
|
||||
<span class="literal number integer">1j</span><span class="operator">*</span><span class="name">Z</span>
|
||||
<span class="name">Z</span><span class="operator">/</span><span class="literal number integer">1</span><span class="operator">/</span><span class="literal number integer">1</span>
|
||||
<span class="name">Z</span><span class="operator"><</span><span class="name">Z</span><span class="operator">></span><span class="name">Z</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">What are the result of the following expressions?</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="name">np</span><span class="operator">.</span><span class="name">array</span><span class="punctuation">(</span><span class="literal number integer">0</span><span class="punctuation">)</span> <span class="operator">//</span> <span class="name">np</span><span class="operator">.</span><span class="name">array</span><span class="punctuation">(</span><span class="literal number integer">0</span><span class="punctuation">)</span>
|
||||
|
||||
<span class="name">np</span><span class="operator">.</span><span class="name">array</span><span class="punctuation">(</span><span class="literal number integer">0</span><span class="punctuation">)</span> <span class="operator">//</span> <span class="name">np</span><span class="operator">.</span><span class="name">array</span><span class="punctuation">(</span><span class="literal number float">0.</span><span class="punctuation">)</span>
|
||||
<span class="name">np</span><span class="operator">.</span><span class="name">array</span><span class="punctuation">(</span><span class="literal number integer">0</span><span class="punctuation">)</span> <span class="operator">/</span> <span class="name">np</span><span class="operator">.</span><span class="name">array</span><span class="punctuation">(</span><span class="literal number integer">0</span><span class="punctuation">)</span>
|
||||
<span class="name">np</span><span class="operator">.</span><span class="name">array</span><span class="punctuation">(</span><span class="literal number integer">0</span><span class="punctuation">)</span> <span class="operator">/</span> <span class="name">np</span><span class="operator">.</span><span class="name">array</span><span class="punctuation">(</span><span class="literal number float">0.</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">How to round away from zero a float array ? (★☆☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Charles R Harris</span>
|
||||
|
||||
<span class="name">Z</span> <span class="operator">=</span> <span class="name">np</span><span class="operator">.</span><span class="name">random</span><span class="operator">.</span><span class="name">uniform</span><span class="punctuation">(</span><span class="operator">-</span><span class="literal number integer">10</span><span class="punctuation">,</span><span class="operator">+</span><span class="literal number integer">10</span><span class="punctuation">,</span><span class="literal number integer">10</span><span class="punctuation">)</span>
|
||||
<span class="keyword">print</span> <span class="punctuation">(</span><span class="name">np</span><span class="operator">.</span><span class="name">trunc</span><span class="punctuation">(</span><span class="name">Z</span> <span class="operator">+</span> <span class="name">np</span><span class="operator">.</span><span class="name">copysign</span><span class="punctuation">(</span><span class="literal number float">0.5</span><span class="punctuation">,</span> <span class="name">Z</span><span class="punctuation">)))</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Extract the integer part of a random array using 5 different methods (★★☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="name">Z</span> <span class="operator">=</span> <span class="name">np</span><span class="operator">.</span><span class="name">random</span><span class="operator">.</span><span class="name">uniform</span><span class="punctuation">(</span><span class="literal number integer">0</span><span class="punctuation">,</span><span class="literal number integer">10</span><span class="punctuation">,</span><span class="literal number integer">10</span><span class="punctuation">)</span>
|
||||
|
||||
<span class="keyword">print</span> <span class="punctuation">(</span><span class="name">Z</span> <span class="operator">-</span> <span class="name">Z</span><span class="operator">%</span><span class="literal number integer">1</span><span class="punctuation">)</span>
|
||||
<span class="keyword">print</span> <span class="punctuation">(</span><span class="name">np</span><span class="operator">.</span><span class="name">floor</span><span class="punctuation">(</span><span class="name">Z</span><span class="punctuation">))</span>
|
||||
<span class="keyword">print</span> <span class="punctuation">(</span><span class="name">np</span><span class="operator">.</span><span class="name">ceil</span><span class="punctuation">(</span><span class="name">Z</span><span class="punctuation">)</span><span class="operator">-</span><span class="literal number integer">1</span><span class="punctuation">)</span>
|
||||
<span class="keyword">print</span> <span class="punctuation">(</span><span class="name">Z</span><span class="operator">.</span><span class="name">astype</span><span class="punctuation">(</span><span class="name builtin">int</span><span class="punctuation">))</span>
|
||||
<span class="keyword">print</span> <span class="punctuation">(</span><span class="name">np</span><span class="operator">.</span><span class="name">trunc</span><span class="punctuation">(</span><span class="name">Z</span><span class="punctuation">))</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Create a 5x5 matrix with row values ranging from 0 to 4 (★★☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="name">Z</span> <span class="operator">=</span> <span class="name">np</span><span class="operator">.</span><span class="name">zeros</span><span class="punctuation">((</span><span class="literal number integer">5</span><span class="punctuation">,</span><span class="literal number integer">5</span><span class="punctuation">))</span>
|
||||
@ -202,7 +257,7 @@ array (★☆☆)</p>
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">Z</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">How to sum a small array faster than np.sum ? (★★☆)</p>
|
||||
<li><p class="first">How to sum a small array faster than np.sum? (★★☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Evgeni Burovski</span>
|
||||
|
||||
@ -273,14 +328,14 @@ them to polar coordinates (★★☆)</p>
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">np</span><span class="operator">.</span><span class="name">finfo</span><span class="punctuation">(</span><span class="name">dtype</span><span class="punctuation">)</span><span class="operator">.</span><span class="name">eps</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">How to print all the values of an array ? (★★☆)</p>
|
||||
<li><p class="first">How to print all the values of an array? (★★☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="name">np</span><span class="operator">.</span><span class="name">set_printoptions</span><span class="punctuation">(</span><span class="name">threshold</span><span class="operator">=</span><span class="name">np</span><span class="operator">.</span><span class="name">nan</span><span class="punctuation">)</span>
|
||||
<span class="name">Z</span> <span class="operator">=</span> <span class="name">np</span><span class="operator">.</span><span class="name">zeros</span><span class="punctuation">((</span><span class="literal number integer">25</span><span class="punctuation">,</span><span class="literal number integer">25</span><span class="punctuation">))</span>
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">Z</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">How to find the closest value (to a given scalar) in an array ? (★★☆)</p>
|
||||
<li><p class="first">How to find the closest value (to a given scalar) in an array? (★★☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="name">Z</span> <span class="operator">=</span> <span class="name">np</span><span class="operator">.</span><span class="name">arange</span><span class="punctuation">(</span><span class="literal number integer">100</span><span class="punctuation">)</span>
|
||||
<span class="name">v</span> <span class="operator">=</span> <span class="name">np</span><span class="operator">.</span><span class="name">random</span><span class="operator">.</span><span class="name">uniform</span><span class="punctuation">(</span><span class="literal number integer">0</span><span class="punctuation">,</span><span class="literal number integer">100</span><span class="punctuation">)</span>
|
||||
@ -316,24 +371,25 @@ point by point distances (★★☆)</p>
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">D</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">How to convert a float (32 bits) array into an integer (32 bits) in place ?</p>
|
||||
<li><p class="first">How to convert a float (32 bits) array into an integer (32 bits) in place?</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="name">Z</span> <span class="operator">=</span> <span class="name">np</span><span class="operator">.</span><span class="name">arange</span><span class="punctuation">(</span><span class="literal number integer">10</span><span class="punctuation">,</span> <span class="name">dtype</span><span class="operator">=</span><span class="name">np</span><span class="operator">.</span><span class="name">int32</span><span class="punctuation">)</span>
|
||||
<span class="name">Z</span> <span class="operator">=</span> <span class="name">Z</span><span class="operator">.</span><span class="name">astype</span><span class="punctuation">(</span><span class="name">np</span><span class="operator">.</span><span class="name">float32</span><span class="punctuation">,</span> <span class="name">copy</span><span class="operator">=</span><span class="name builtin pseudo">False</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Consider the following file:</p>
|
||||
<pre class="literal-block">
|
||||
1,2,3,4,5
|
||||
6,,,7,8
|
||||
,,9,10,11
|
||||
</pre>
|
||||
<p>How to read it ? (★★☆)</p>
|
||||
<li><p class="first">How to read the following file? (★★☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># File content:</span>
|
||||
<span class="comment single"># -------------</span>
|
||||
<span class="literal number integer">1</span><span class="punctuation">,</span><span class="literal number integer">2</span><span class="punctuation">,</span><span class="literal number integer">3</span><span class="punctuation">,</span><span class="literal number integer">4</span><span class="punctuation">,</span><span class="literal number integer">5</span>
|
||||
<span class="literal number integer">6</span><span class="punctuation">,,,</span><span class="literal number integer">7</span><span class="punctuation">,</span><span class="literal number integer">8</span>
|
||||
<span class="punctuation">,,</span><span class="literal number integer">9</span><span class="punctuation">,</span><span class="literal number integer">10</span><span class="punctuation">,</span><span class="literal number integer">11</span>
|
||||
<span class="comment single"># -------------</span>
|
||||
|
||||
<span class="name">Z</span> <span class="operator">=</span> <span class="name">np</span><span class="operator">.</span><span class="name">genfromtxt</span><span class="punctuation">(</span><span class="literal string double">"missing.dat"</span><span class="punctuation">,</span> <span class="name">delimiter</span><span class="operator">=</span><span class="literal string double">","</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">What is the equivalent of <cite>enumerate</cite> for numpy arrays ? (★★☆)</p>
|
||||
<li><p class="first">What is the equivalent of <cite>enumerate</cite> for numpy arrays? (★★☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="name">Z</span> <span class="operator">=</span> <span class="name">np</span><span class="operator">.</span><span class="name">arange</span><span class="punctuation">(</span><span class="literal number integer">9</span><span class="punctuation">)</span><span class="operator">.</span><span class="name">reshape</span><span class="punctuation">(</span><span class="literal number integer">3</span><span class="punctuation">,</span><span class="literal number integer">3</span><span class="punctuation">)</span>
|
||||
<span class="keyword">for</span> <span class="name">index</span><span class="punctuation">,</span> <span class="name">value</span> <span class="operator word">in</span> <span class="name">np</span><span class="operator">.</span><span class="name">ndenumerate</span><span class="punctuation">(</span><span class="name">Z</span><span class="punctuation">):</span>
|
||||
@ -351,7 +407,7 @@ point by point distances (★★☆)</p>
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">G</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">How to randomly place p elements in a 2D array ? (★★☆)</p>
|
||||
<li><p class="first">How to randomly place p elements in a 2D array? (★★☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Divakar</span>
|
||||
|
||||
@ -374,7 +430,7 @@ point by point distances (★★☆)</p>
|
||||
<span class="name">Y</span> <span class="operator">=</span> <span class="name">X</span> <span class="operator">-</span> <span class="name">X</span><span class="operator">.</span><span class="name">mean</span><span class="punctuation">(</span><span class="name">axis</span><span class="operator">=</span><span class="literal number integer">1</span><span class="punctuation">)</span><span class="operator">.</span><span class="name">reshape</span><span class="punctuation">(</span><span class="operator">-</span><span class="literal number integer">1</span><span class="punctuation">,</span> <span class="literal number integer">1</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">How to I sort an array by the nth column ? (★★☆)</p>
|
||||
<li><p class="first">How to I sort an array by the nth column? (★★☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Steve Tjoa</span>
|
||||
|
||||
@ -383,7 +439,7 @@ point by point distances (★★☆)</p>
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">Z</span><span class="punctuation">[</span><span class="name">Z</span><span class="punctuation">[:,</span><span class="literal number integer">1</span><span class="punctuation">]</span><span class="operator">.</span><span class="name">argsort</span><span class="punctuation">()])</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">How to tell if a given 2D array has null columns ? (★★☆)</p>
|
||||
<li><p class="first">How to tell if a given 2D array has null columns? (★★☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Warren Weckesser</span>
|
||||
|
||||
@ -399,8 +455,23 @@ point by point distances (★★☆)</p>
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">m</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Create an array class that has a <cite>name</cite> attribute (★★☆)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="keyword">class</span> <span class="name class">NamedArray</span><span class="punctuation">(</span><span class="name">np</span><span class="operator">.</span><span class="name">ndarray</span><span class="punctuation">):</span>
|
||||
<span class="keyword">def</span> <span class="name function">__new__</span><span class="punctuation">(</span><span class="name">cls</span><span class="punctuation">,</span> <span class="name">array</span><span class="punctuation">,</span> <span class="name">name</span><span class="operator">=</span><span class="literal string double">"no name"</span><span class="punctuation">):</span>
|
||||
<span class="name">obj</span> <span class="operator">=</span> <span class="name">np</span><span class="operator">.</span><span class="name">asarray</span><span class="punctuation">(</span><span class="name">array</span><span class="punctuation">)</span><span class="operator">.</span><span class="name">view</span><span class="punctuation">(</span><span class="name">cls</span><span class="punctuation">)</span>
|
||||
<span class="name">obj</span><span class="operator">.</span><span class="name">name</span> <span class="operator">=</span> <span class="name">name</span>
|
||||
<span class="keyword">return</span> <span class="name">obj</span>
|
||||
<span class="keyword">def</span> <span class="name function">__array_finalize__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">obj</span><span class="punctuation">):</span>
|
||||
<span class="keyword">if</span> <span class="name">obj</span> <span class="operator word">is</span> <span class="name builtin pseudo">None</span><span class="punctuation">:</span> <span class="keyword">return</span>
|
||||
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">info</span> <span class="operator">=</span> <span class="name builtin">getattr</span><span class="punctuation">(</span><span class="name">obj</span><span class="punctuation">,</span> <span class="literal string single">'name'</span><span class="punctuation">,</span> <span class="literal string double">"no name"</span><span class="punctuation">)</span>
|
||||
|
||||
<span class="name">Z</span> <span class="operator">=</span> <span class="name">NamedArray</span><span class="punctuation">(</span><span class="name">np</span><span class="operator">.</span><span class="name">arange</span><span class="punctuation">(</span><span class="literal number integer">10</span><span class="punctuation">),</span> <span class="literal string double">"range_10"</span><span class="punctuation">)</span>
|
||||
<span class="keyword">print</span> <span class="punctuation">(</span><span class="name">Z</span><span class="operator">.</span><span class="name">name</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Consider a given vector, how to add 1 to each element indexed by a second
|
||||
vector (be careful with repeated indices) ? (★★★)</p>
|
||||
vector (be careful with repeated indices)? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Brett Olsen</span>
|
||||
|
||||
@ -411,7 +482,7 @@ vector (be careful with repeated indices) ? (★★★)</p>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">How to accumulate elements of a vector (X) to an array (F) based on an index
|
||||
list (I) ? (★★★)</p>
|
||||
list (I)? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Alan G Isaac</span>
|
||||
|
||||
@ -434,7 +505,7 @@ colors (★★★)</p>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Considering a four dimensions array, how to get sum over the last two axis
|
||||
at once ? (★★★)</p>
|
||||
at once? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="name">A</span> <span class="operator">=</span> <span class="name">np</span><span class="operator">.</span><span class="name">random</span><span class="operator">.</span><span class="name">randint</span><span class="punctuation">(</span><span class="literal number integer">0</span><span class="punctuation">,</span><span class="literal number integer">10</span><span class="punctuation">,(</span><span class="literal number integer">3</span><span class="punctuation">,</span><span class="literal number integer">4</span><span class="punctuation">,</span><span class="literal number integer">3</span><span class="punctuation">,</span><span class="literal number integer">4</span><span class="punctuation">))</span>
|
||||
<span class="name builtin">sum</span> <span class="operator">=</span> <span class="name">A</span><span class="operator">.</span><span class="name">reshape</span><span class="punctuation">(</span><span class="name">A</span><span class="operator">.</span><span class="name">shape</span><span class="punctuation">[:</span><span class="operator">-</span><span class="literal number integer">2</span><span class="punctuation">]</span> <span class="operator">+</span> <span class="punctuation">(</span><span class="operator">-</span><span class="literal number integer">1</span><span class="punctuation">,))</span><span class="operator">.</span><span class="name">sum</span><span class="punctuation">(</span><span class="name">axis</span><span class="operator">=-</span><span class="literal number integer">1</span><span class="punctuation">)</span>
|
||||
@ -442,7 +513,7 @@ at once ? (★★★)</p>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Considering a one-dimensional vector D, how to compute means of subsets of D
|
||||
using a vector S of same size describing subset indices ? (★★★)</p>
|
||||
using a vector S of same size describing subset indices? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Jaime Fernández del Río</span>
|
||||
|
||||
@ -454,7 +525,7 @@ using a vector S of same size describing subset indices ? (★★★)</p>
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">D_means</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">How to get the diagonal of a dot product ? (★★★)</p>
|
||||
<li><p class="first">How to get the diagonal of a dot product? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Mathieu Blondel</span>
|
||||
|
||||
@ -469,7 +540,7 @@ using a vector S of same size describing subset indices ? (★★★)</p>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Consider the vector [1, 2, 3, 4, 5], how to build a new vector with 3
|
||||
consecutive zeros interleaved between each value ? (★★★)</p>
|
||||
consecutive zeros interleaved between each value? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Warren Weckesser</span>
|
||||
|
||||
@ -481,14 +552,14 @@ consecutive zeros interleaved between each value ? (★★★)</p>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Consider an array of dimension (5,5,3), how to mulitply it by an array with
|
||||
dimensions (5,5) ? (★★★)</p>
|
||||
dimensions (5,5)? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="name">A</span> <span class="operator">=</span> <span class="name">np</span><span class="operator">.</span><span class="name">ones</span><span class="punctuation">((</span><span class="literal number integer">5</span><span class="punctuation">,</span><span class="literal number integer">5</span><span class="punctuation">,</span><span class="literal number integer">3</span><span class="punctuation">))</span>
|
||||
<span class="name">B</span> <span class="operator">=</span> <span class="literal number integer">2</span><span class="operator">*</span><span class="name">np</span><span class="operator">.</span><span class="name">ones</span><span class="punctuation">((</span><span class="literal number integer">5</span><span class="punctuation">,</span><span class="literal number integer">5</span><span class="punctuation">))</span>
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">A</span> <span class="operator">*</span> <span class="name">B</span><span class="punctuation">[:,:,</span><span class="name builtin pseudo">None</span><span class="punctuation">])</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">How to swap two rows of an array ? (★★★)</p>
|
||||
<li><p class="first">How to swap two rows of an array? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Eelco Hoogendoorn</span>
|
||||
|
||||
@ -512,7 +583,7 @@ vertices), find the set of unique line segments composing all the triangles (★
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Given an array C that is a bincount, how to produce an array A such that
|
||||
np.bincount(A) == C ? (★★★)</p>
|
||||
np.bincount(A) == C? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Jaime Fernández del Río</span>
|
||||
|
||||
@ -521,7 +592,7 @@ np.bincount(A) == C ? (★★★)</p>
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">A</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">How to compute averages using a sliding window over an array ? (★★★)</p>
|
||||
<li><p class="first">How to compute averages using a sliding window over an array? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Jaime Fernández del Río</span>
|
||||
|
||||
@ -548,7 +619,7 @@ row should be (Z[-3],Z[-2],Z[-1]) (★★★)</p>
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">Z</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">How to negate a boolean, or to change the sign of a float inplace ? (★★★)</p>
|
||||
<li><p class="first">How to negate a boolean, or to change the sign of a float inplace? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Nathaniel J. Smith</span>
|
||||
|
||||
@ -560,7 +631,7 @@ row should be (Z[-3],Z[-2],Z[-1]) (★★★)</p>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Consider 2 sets of points P0,P1 describing lines (2d) and a point p, how to
|
||||
compute distance from p to each line i (P0[i],P1[i]) ? (★★★)</p>
|
||||
compute distance from p to each line i (P0[i],P1[i])? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="keyword">def</span> <span class="name function">distance</span><span class="punctuation">(</span><span class="name">P0</span><span class="punctuation">,</span> <span class="name">P1</span><span class="punctuation">,</span> <span class="name">p</span><span class="punctuation">):</span>
|
||||
<span class="name">T</span> <span class="operator">=</span> <span class="name">P1</span> <span class="operator">-</span> <span class="name">P0</span>
|
||||
@ -577,7 +648,7 @@ compute distance from p to each line i (P0[i],P1[i]) ? (★★★)</p>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Consider 2 sets of points P0,P1 describing lines (2d) and a set of points P,
|
||||
how to compute distance from each point j (P[j]) to each line i (P0[i],P1[i]) ? (★★★)</p>
|
||||
how to compute distance from each point j (P[j]) to each line i (P0[i],P1[i])? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Italmassov Kuanysh</span>
|
||||
<span class="comment single"># based on distance function from previous question</span>
|
||||
@ -621,7 +692,7 @@ necessary) (★★★)</p>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Consider an array Z = [1,2,3,4,5,6,7,8,9,10,11,12,13,14], how to generate an
|
||||
array R = [[1,2,3,4], [2,3,4,5], [3,4,5,6], ..., [11,12,13,14]] ? (★★★)</p>
|
||||
array R = [[1,2,3,4], [2,3,4,5], [3,4,5,6], ..., [11,12,13,14]]? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Stefan van der Walt</span>
|
||||
|
||||
@ -639,7 +710,7 @@ array R = [[1,2,3,4], [2,3,4,5], [3,4,5,6], ..., [11,12,13,14]] ? (★★★)</p
|
||||
<span class="name">rank</span> <span class="operator">=</span> <span class="name">np</span><span class="operator">.</span><span class="name">sum</span><span class="punctuation">(</span><span class="name">S</span> <span class="operator">></span> <span class="literal number float">1e-10</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">How to find the most frequent value in an array ?</p>
|
||||
<li><p class="first">How to find the most frequent value in an array?</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="name">Z</span> <span class="operator">=</span> <span class="name">np</span><span class="operator">.</span><span class="name">random</span><span class="operator">.</span><span class="name">randint</span><span class="punctuation">(</span><span class="literal number integer">0</span><span class="punctuation">,</span><span class="literal number integer">10</span><span class="punctuation">,</span><span class="literal number integer">50</span><span class="punctuation">)</span>
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">np</span><span class="operator">.</span><span class="name">bincount</span><span class="punctuation">(</span><span class="name">Z</span><span class="punctuation">)</span><span class="operator">.</span><span class="name">argmax</span><span class="punctuation">())</span>
|
||||
@ -676,7 +747,7 @@ array R = [[1,2,3,4], [2,3,4,5], [3,4,5,6], ..., [11,12,13,14]] ? (★★★)</p
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Consider a set of p matrices wich shape (n,n) and a set of p vectors with shape (n,1).
|
||||
How to compute the sum of of the p matrix products at once ? (result has shape (n,1)) (★★★)</p>
|
||||
How to compute the sum of of the p matrix products at once? (result has shape (n,1)) (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Stefan van der Walt</span>
|
||||
|
||||
@ -693,7 +764,7 @@ How to compute the sum of of the p matrix products at once ? (result has shape (
|
||||
<span class="comment single"># and 2 and 1, to remain with a (n,1) vector.</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Consider a 16x16 array, how to get the block-sum (block size is 4x4) ? (★★★)</p>
|
||||
<li><p class="first">Consider a 16x16 array, how to get the block-sum (block size is 4x4)? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Robert Kern</span>
|
||||
|
||||
@ -703,7 +774,7 @@ How to compute the sum of of the p matrix products at once ? (result has shape (
|
||||
<span class="name">np</span><span class="operator">.</span><span class="name">arange</span><span class="punctuation">(</span><span class="literal number integer">0</span><span class="punctuation">,</span> <span class="name">Z</span><span class="operator">.</span><span class="name">shape</span><span class="punctuation">[</span><span class="literal number integer">1</span><span class="punctuation">],</span> <span class="name">k</span><span class="punctuation">),</span> <span class="name">axis</span><span class="operator">=</span><span class="literal number integer">1</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">How to implement the Game of Life using numpy arrays ? (★★★)</p>
|
||||
<li><p class="first">How to implement the Game of Life using numpy arrays? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Nicolas Rougier</span>
|
||||
|
||||
@ -757,7 +828,7 @@ combinations of every item) (★★★)</p>
|
||||
<span class="keyword">print</span> <span class="punctuation">(</span><span class="name">cartesian</span><span class="punctuation">(([</span><span class="literal number integer">1</span><span class="punctuation">,</span> <span class="literal number integer">2</span><span class="punctuation">,</span> <span class="literal number integer">3</span><span class="punctuation">],</span> <span class="punctuation">[</span><span class="literal number integer">4</span><span class="punctuation">,</span> <span class="literal number integer">5</span><span class="punctuation">],</span> <span class="punctuation">[</span><span class="literal number integer">6</span><span class="punctuation">,</span> <span class="literal number integer">7</span><span class="punctuation">])))</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">How to create a record array from a regular array ? (★★★)</p>
|
||||
<li><p class="first">How to create a record array from a regular array? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="name">Z</span> <span class="operator">=</span> <span class="name">np</span><span class="operator">.</span><span class="name">array</span><span class="punctuation">([(</span><span class="literal string double">"Hello"</span><span class="punctuation">,</span> <span class="literal number float">2.5</span><span class="punctuation">,</span> <span class="literal number integer">3</span><span class="punctuation">),</span>
|
||||
<span class="punctuation">(</span><span class="literal string double">"World"</span><span class="punctuation">,</span> <span class="literal number float">3.6</span><span class="punctuation">,</span> <span class="literal number integer">2</span><span class="punctuation">)])</span>
|
||||
@ -766,7 +837,7 @@ combinations of every item) (★★★)</p>
|
||||
<span class="name">formats</span> <span class="operator">=</span> <span class="literal string single">'S8, f8, i8'</span><span class="punctuation">)</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Comsider a large vector Z, compute Z to the power of 3 using 3 different
|
||||
<li><p class="first">Consider a large vector Z, compute Z to the power of 3 using 3 different
|
||||
methods (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="name">Author</span><span class="punctuation">:</span> <span class="name">Ryan</span> <span class="name">G</span><span class="operator">.</span>
|
||||
@ -785,7 +856,7 @@ methods (★★★)</p>
|
||||
</li>
|
||||
<li><p class="first">Consider two arrays A and B of shape (8,3) and (2,2). How to find rows of A
|
||||
that contain elements of each row of B regardless of the order of the elements
|
||||
in B ? (★★★)</p>
|
||||
in B? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Gabe Schwartz</span>
|
||||
|
||||
@ -822,7 +893,7 @@ in B ? (★★★)</p>
|
||||
<span class="keyword">print</span><span class="punctuation">(</span><span class="name">np</span><span class="operator">.</span><span class="name">unpackbits</span><span class="punctuation">(</span><span class="name">I</span><span class="punctuation">[:,</span> <span class="name">np</span><span class="operator">.</span><span class="name">newaxis</span><span class="punctuation">],</span> <span class="name">axis</span><span class="operator">=</span><span class="literal number integer">1</span><span class="punctuation">))</span>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Given a two dimensional array, how to extract unique rows ? (★★★)</p>
|
||||
<li><p class="first">Given a two dimensional array, how to extract unique rows? (★★★)</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Jaime Fernández del Río</span>
|
||||
|
||||
@ -846,7 +917,7 @@ sum, and mul function (★★★)</p>
|
||||
</pre>
|
||||
</li>
|
||||
<li><p class="first">Considering a path described by two vectors (X,Y), how to sample it using
|
||||
equidistant samples (★★★) ?</p>
|
||||
equidistant samples (★★★)?</p>
|
||||
<pre class="code python literal-block">
|
||||
<span class="comment single"># Author: Bas Swinckels</span>
|
||||
|
||||
|
||||
162
README.rst
162
README.rst
@ -52,7 +52,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
print(Z)
|
||||
|
||||
|
||||
#. How to get the documentation of the numpy add function from the command line ? (★☆☆)
|
||||
#. How to get the documentation of the numpy add function from the command line? (★☆☆)
|
||||
|
||||
.. code-block:: bash
|
||||
|
||||
@ -142,7 +142,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
Z[1:-1,1:-1] = 0
|
||||
|
||||
|
||||
#. What is the result of the following expression ? (★☆☆)
|
||||
#. What is the result of the following expression? (★☆☆)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -170,7 +170,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
Z[::2,1::2] = 1
|
||||
print(Z)
|
||||
|
||||
#. Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element ?
|
||||
#. Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element?
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -193,6 +193,14 @@ Thanks to Michiaki Ariga, there is now a
|
||||
Z = (Z - Zmin)/(Zmax - Zmin)
|
||||
print(Z)
|
||||
|
||||
#. Create a custom dtype that describes a color as four unisgned bytes (RGBA) (★☆☆)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
color = np.dtype([("r", np.ubyte, 1),
|
||||
("g", np.ubyte, 1),
|
||||
("b", np.ubyte, 1),
|
||||
("a", np.ubyte, 1)])
|
||||
|
||||
#. Multiply a 5x3 matrix by a 3x2 matrix (real matrix product) (★☆☆)
|
||||
|
||||
@ -201,7 +209,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
Z = np.dot(np.ones((5,3)), np.ones((3,2)))
|
||||
print(Z)
|
||||
|
||||
#. Given a 1D array, negate all elements which are between 3 and 8, in place. (★☆☆)
|
||||
#. Given a 1D array, negate all elements which are between 3 and 8, in place. (★☆☆)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -210,6 +218,59 @@ Thanks to Michiaki Ariga, there is now a
|
||||
Z = np.arange(11)
|
||||
Z[(3 < Z) & (Z <= 8)] *= -1
|
||||
|
||||
#. What is the output of the following script? (★☆☆)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
# Author: Jake VanderPlas
|
||||
|
||||
print(sum(range(5),-1))
|
||||
from numpy import *
|
||||
print(sum(range(5),-1))
|
||||
|
||||
#. Consider an integer vector Z, which of these expressions are legal? (★☆☆)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
Z**Z
|
||||
2 << Z >> 2
|
||||
Z <- Z
|
||||
1j*Z
|
||||
Z/1/1
|
||||
Z<Z>Z
|
||||
|
||||
#. What are the result of the following expressions?
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
np.array(0) // np.array(0)
|
||||
|
||||
np.array(0) // np.array(0.)
|
||||
np.array(0) / np.array(0)
|
||||
np.array(0) / np.array(0.)
|
||||
|
||||
#. How to round away from zero a float array ? (★☆☆)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
# Author: Charles R Harris
|
||||
|
||||
Z = np.random.uniform(-10,+10,10)
|
||||
print (np.trunc(Z + np.copysign(0.5, Z)))
|
||||
|
||||
|
||||
#. Extract the integer part of a random array using 5 different methods (★★☆)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
Z = np.random.uniform(0,10,10)
|
||||
|
||||
print (Z - Z%1)
|
||||
print (np.floor(Z))
|
||||
print (np.ceil(Z)-1)
|
||||
print (Z.astype(int))
|
||||
print (np.trunc(Z))
|
||||
|
||||
|
||||
#. Create a 5x5 matrix with row values ranging from 0 to 4 (★★☆)
|
||||
|
||||
@ -249,7 +310,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
print(Z)
|
||||
|
||||
|
||||
#. How to sum a small array faster than np.sum ? (★★☆)
|
||||
#. How to sum a small array faster than np.sum? (★★☆)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -336,7 +397,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
print(np.finfo(dtype).max)
|
||||
print(np.finfo(dtype).eps)
|
||||
|
||||
#. How to print all the values of an array ? (★★☆)
|
||||
#. How to print all the values of an array? (★★☆)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -345,7 +406,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
print(Z)
|
||||
|
||||
|
||||
#. How to find the closest value (to a given scalar) in an array ? (★★☆)
|
||||
#. How to find the closest value (to a given scalar) in an array? (★★☆)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -386,7 +447,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
print(D)
|
||||
|
||||
|
||||
#. How to convert a float (32 bits) array into an integer (32 bits) in place ?
|
||||
#. How to convert a float (32 bits) array into an integer (32 bits) in place?
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -394,20 +455,21 @@ Thanks to Michiaki Ariga, there is now a
|
||||
Z = Z.astype(np.float32, copy=False)
|
||||
|
||||
|
||||
#. Consider the following file::
|
||||
|
||||
1,2,3,4,5
|
||||
6,,,7,8
|
||||
,,9,10,11
|
||||
|
||||
How to read it ? (★★☆)
|
||||
#. How to read the following file? (★★☆)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
# File content:
|
||||
# -------------
|
||||
1,2,3,4,5
|
||||
6,,,7,8
|
||||
,,9,10,11
|
||||
# -------------
|
||||
|
||||
Z = np.genfromtxt("missing.dat", delimiter=",")
|
||||
|
||||
|
||||
#. What is the equivalent of `enumerate` for numpy arrays ? (★★☆)
|
||||
#. What is the equivalent of `enumerate` for numpy arrays? (★★☆)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -428,7 +490,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
G = np.exp(-( (D-mu)**2 / ( 2.0 * sigma**2 ) ) )
|
||||
print(G)
|
||||
|
||||
#. How to randomly place p elements in a 2D array ? (★★☆)
|
||||
#. How to randomly place p elements in a 2D array? (★★☆)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -453,7 +515,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
# Older versions of numpy
|
||||
Y = X - X.mean(axis=1).reshape(-1, 1)
|
||||
|
||||
#. How to I sort an array by the nth column ? (★★☆)
|
||||
#. How to I sort an array by the nth column? (★★☆)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -464,7 +526,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
print(Z[Z[:,1].argsort()])
|
||||
|
||||
|
||||
#. How to tell if a given 2D array has null columns ? (★★☆)
|
||||
#. How to tell if a given 2D array has null columns? (★★☆)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -483,12 +545,27 @@ Thanks to Michiaki Ariga, there is now a
|
||||
m = Z.flat[np.abs(Z - z).argmin()]
|
||||
print(m)
|
||||
|
||||
|
||||
#. Create an array class that has a `name` attribute (★★☆)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
class NamedArray(np.ndarray):
|
||||
def __new__(cls, array, name="no name"):
|
||||
obj = np.asarray(array).view(cls)
|
||||
obj.name = name
|
||||
return obj
|
||||
def __array_finalize__(self, obj):
|
||||
if obj is None: return
|
||||
self.info = getattr(obj, 'name', "no name")
|
||||
|
||||
Z = NamedArray(np.arange(10), "range_10")
|
||||
print (Z.name)
|
||||
|
||||
|
||||
|
||||
#. Consider a given vector, how to add 1 to each element indexed by a second
|
||||
vector (be careful with repeated indices) ? (★★★)
|
||||
vector (be careful with repeated indices)? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -501,7 +578,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
|
||||
|
||||
#. How to accumulate elements of a vector (X) to an array (F) based on an index
|
||||
list (I) ? (★★★)
|
||||
list (I)? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -528,7 +605,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
|
||||
|
||||
#. Considering a four dimensions array, how to get sum over the last two axis
|
||||
at once ? (★★★)
|
||||
at once? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -538,7 +615,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
|
||||
|
||||
#. Considering a one-dimensional vector D, how to compute means of subsets of D
|
||||
using a vector S of same size describing subset indices ? (★★★)
|
||||
using a vector S of same size describing subset indices? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -552,7 +629,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
print(D_means)
|
||||
|
||||
|
||||
#. How to get the diagonal of a dot product ? (★★★)
|
||||
#. How to get the diagonal of a dot product? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -569,7 +646,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
|
||||
|
||||
#. Consider the vector [1, 2, 3, 4, 5], how to build a new vector with 3
|
||||
consecutive zeros interleaved between each value ? (★★★)
|
||||
consecutive zeros interleaved between each value? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -583,7 +660,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
|
||||
|
||||
#. Consider an array of dimension (5,5,3), how to mulitply it by an array with
|
||||
dimensions (5,5) ? (★★★)
|
||||
dimensions (5,5)? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -592,7 +669,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
print(A * B[:,:,None])
|
||||
|
||||
|
||||
#. How to swap two rows of an array ? (★★★)
|
||||
#. How to swap two rows of an array? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -620,7 +697,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
|
||||
|
||||
#. Given an array C that is a bincount, how to produce an array A such that
|
||||
np.bincount(A) == C ? (★★★)
|
||||
np.bincount(A) == C? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -631,7 +708,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
print(A)
|
||||
|
||||
|
||||
#. How to compute averages using a sliding window over an array ? (★★★)
|
||||
#. How to compute averages using a sliding window over an array? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -661,7 +738,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
print(Z)
|
||||
|
||||
|
||||
#. How to negate a boolean, or to change the sign of a float inplace ? (★★★)
|
||||
#. How to negate a boolean, or to change the sign of a float inplace? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -676,7 +753,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
|
||||
|
||||
#. Consider 2 sets of points P0,P1 describing lines (2d) and a point p, how to
|
||||
compute distance from p to each line i (P0[i],P1[i]) ? (★★★)
|
||||
compute distance from p to each line i (P0[i],P1[i])? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -695,7 +772,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
|
||||
|
||||
#. Consider 2 sets of points P0,P1 describing lines (2d) and a set of points P,
|
||||
how to compute distance from each point j (P[j]) to each line i (P0[i],P1[i]) ? (★★★)
|
||||
how to compute distance from each point j (P[j]) to each line i (P0[i],P1[i])? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -742,7 +819,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
|
||||
|
||||
#. Consider an array Z = [1,2,3,4,5,6,7,8,9,10,11,12,13,14], how to generate an
|
||||
array R = [[1,2,3,4], [2,3,4,5], [3,4,5,6], ..., [11,12,13,14]] ? (★★★)
|
||||
array R = [[1,2,3,4], [2,3,4,5], [3,4,5,6], ..., [11,12,13,14]]? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -762,7 +839,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
U, S, V = np.linalg.svd(Z) # Singular Value Decomposition
|
||||
rank = np.sum(S > 1e-10)
|
||||
|
||||
#. How to find the most frequent value in an array ?
|
||||
#. How to find the most frequent value in an array?
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -803,7 +880,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
print(S)
|
||||
|
||||
#. Consider a set of p matrices wich shape (n,n) and a set of p vectors with shape (n,1).
|
||||
How to compute the sum of of the p matrix products at once ? (result has shape (n,1)) (★★★)
|
||||
How to compute the sum of of the p matrix products at once? (result has shape (n,1)) (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -822,7 +899,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
# and 2 and 1, to remain with a (n,1) vector.
|
||||
|
||||
|
||||
#. Consider a 16x16 array, how to get the block-sum (block size is 4x4) ? (★★★)
|
||||
#. Consider a 16x16 array, how to get the block-sum (block size is 4x4)? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -834,7 +911,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
np.arange(0, Z.shape[1], k), axis=1)
|
||||
|
||||
|
||||
#. How to implement the Game of Life using numpy arrays ? (★★★)
|
||||
#. How to implement the Game of Life using numpy arrays? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -893,7 +970,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
print (cartesian(([1, 2, 3], [4, 5], [6, 7])))
|
||||
|
||||
|
||||
#. How to create a record array from a regular array ? (★★★)
|
||||
#. How to create a record array from a regular array? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -903,7 +980,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
names='col1, col2, col3',
|
||||
formats = 'S8, f8, i8')
|
||||
|
||||
#. Comsider a large vector Z, compute Z to the power of 3 using 3 different
|
||||
#. Consider a large vector Z, compute Z to the power of 3 using 3 different
|
||||
methods (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
@ -924,7 +1001,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
|
||||
#. Consider two arrays A and B of shape (8,3) and (2,2). How to find rows of A
|
||||
that contain elements of each row of B regardless of the order of the elements
|
||||
in B ? (★★★)
|
||||
in B? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -951,7 +1028,6 @@ Thanks to Michiaki Ariga, there is now a
|
||||
print(U)
|
||||
|
||||
|
||||
|
||||
#. Convert a vector of ints into a matrix binary representation (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
@ -968,7 +1044,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
print(np.unpackbits(I[:, np.newaxis], axis=1))
|
||||
|
||||
|
||||
#. Given a two dimensional array, how to extract unique rows ? (★★★)
|
||||
#. Given a two dimensional array, how to extract unique rows? (★★★)
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
@ -996,7 +1072,7 @@ Thanks to Michiaki Ariga, there is now a
|
||||
|
||||
|
||||
#. Considering a path described by two vectors (X,Y), how to sample it using
|
||||
equidistant samples (★★★) ?
|
||||
equidistant samples (★★★)?
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user