Added some exercises

2016-07-14 11:55:31 -05:00
parent 26f1f77460
commit 03ccfbdd33
2 changed files with 234 additions and 87 deletions
--- a/README.html
+++ b/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
@@ -158,6 +158,14 @@ python -c <span class="literal string double">&quot;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">&quot;r&quot;</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">&quot;g&quot;</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">&quot;b&quot;</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">&quot;a&quot;</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>
@@ -172,6 +180,53 @@ python -c <span class="literal string double">&quot;import numpy; numpy.info(num
 <span class="name">Z</span><span class="punctuation">[(</span><span class="literal number integer">3</span> <span class="operator">&lt;</span> <span class="name">Z</span><span class="punctuation">)</span> <span class="operator">&amp;</span> <span class="punctuation">(</span><span class="name">Z</span> <span class="operator">&lt;=</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">&lt;&lt;</span> <span class="name">Z</span> <span class="operator">&gt;&gt;</span> <span class="literal number integer">2</span>
+<span class="name">Z</span> <span class="operator">&lt;-</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">&lt;</span><span class="name">Z</span><span class="operator">&gt;</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>
@@ -322,14 +377,15 @@ point by point distances (★★☆)</p>
 <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">&quot;missing.dat&quot;</span><span class="punctuation">,</span> <span class="name">delimiter</span><span class="operator">=</span><span class="literal string double">&quot;,&quot;</span><span class="punctuation">)</span>
 </pre>
 </li>
@@ -399,6 +455,21 @@ 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">&quot;no name&quot;</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">&quot;no name&quot;</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">&quot;range_10&quot;</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>
 <pre class="code python literal-block">
@@ -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>
--- a/README.rst
+++ b/README.rst
@@ -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) (★☆☆) 

@@ -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 (★★☆) 

@@ -394,15 +455,16 @@ Thanks to Michiaki Ariga, there is now a
      Z = Z.astype(np.float32, copy=False)
                   
   
-#. Consider the following file::
+#. How to read the following file? (★★☆)

+   .. code-block:: python
+
+      # File content:
+      # -------------
      1,2,3,4,5
      6,,,7,8
      ,,9,10,11
-
-   How to read it ? (★★☆) 
-
-   .. code-block:: python
+      # -------------

      Z = np.genfromtxt("missing.dat", delimiter=",")

@@ -484,6 +546,21 @@ Thanks to Michiaki Ariga, there is now a
      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)



@@ -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
@@ -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