From 17dcb63add60ad767ac931fac4f6047b48ad9dc4 Mon Sep 17 00:00:00 2001
From: Nicolas Rougier <Nicolas.Rougier@inria.fr>
Date: Tue, 27 May 2014 06:18:00 +0200
Subject: [PATCH] index.txt -> index.rst

---
 index.html => README.html |  23 ++
 README.rst                | 506 ++++++++++++++++++++++++++++++++++++++
 README.txt                |  26 --
 3 files changed, 529 insertions(+), 26 deletions(-)
 rename index.html => README.html (98%)
 create mode 100644 README.rst
 delete mode 100644 README.txt

diff --git a/index.html b/README.html
similarity index 98%
rename from index.html
rename to README.html
index 7865a2c..7bc8533 100644
--- a/index.html
+++ b/README.html
@@ -12,6 +12,27 @@
 <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
+provide also a set of exercices for those who teach. If you remember having
+asked or answered a (short) problem, you can send a pull request. The format
+is:</p>
+<pre class="literal-block">
+#. Find indices of non-zero elements from [1,2,0,0,4,0]
+
+   .. code:: python
+
+      # Author: Somebody
+
+      print np.nonzero([1,2,0,0,4,0])
+</pre>
+<p>Here is what the page looks like so far:
+<a class="reference external" href="http://www.loria.fr/~rougier/teaching/numpy.100/index.html">http://www.loria.fr/~rougier/teaching/numpy.100/index.html</a></p>
+<div class="note">
+<p class="first admonition-title">Note</p>
+<p class="last">The level names came from an old-game (Dungeon Master)</p>
+</div>
+<p>Repository is at: <a class="reference external" href="https://github.com/rougier/numpy-100">https://github.com/rougier/numpy-100</a></p>
+<p><strong>Contents</strong></p>
 <div class="contents local topic" id="contents">
 <ul class="simple">
 <li><a class="reference internal" href="#neophyte" id="id1">Neophyte</a></li>
@@ -290,6 +311,8 @@ colors</p>
 <span class="name">I</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">2</span><span class="punctuation">,(</span><span class="name">h</span><span class="punctuation">,</span><span class="name">w</span><span class="punctuation">,</span><span class="literal number integer">3</span><span class="punctuation">))</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">ubyte</span><span class="punctuation">)</span>
 <span class="name">F</span> <span class="operator">=</span> <span class="name">I</span><span class="punctuation">[</span><span class="operator">...</span><span class="punctuation">,</span><span class="literal number integer">0</span><span class="punctuation">]</span><span class="operator">*</span><span class="literal number integer">256</span><span class="operator">*</span><span class="literal number integer">256</span> <span class="operator">+</span> <span class="name">I</span><span class="punctuation">[</span><span class="operator">...</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">256</span> <span class="operator">+</span><span class="name">I</span><span class="punctuation">[</span><span class="operator">...</span><span class="punctuation">,</span><span class="literal number integer">2</span><span class="punctuation">]</span>
 <span class="name">n</span> <span class="operator">=</span> <span class="name builtin">len</span><span class="punctuation">(</span><span class="name">np</span><span class="operator">.</span><span class="name">unique</span><span class="punctuation">(</span><span class="name">F</span><span class="punctuation">))</span>
+
+<span class="name">np</span><span class="operator">.</span><span class="name">unique</span><span class="punctuation">(</span><span class="name">I</span><span class="punctuation">)</span>
 </pre>
 </li>
 <li><p class="first">Considering a four dimensions array, how to get sum over the last two axis at once ?</p>
diff --git a/README.rst b/README.rst
new file mode 100644
index 0000000..a756281
--- /dev/null
+++ b/README.rst
@@ -0,0 +1,506 @@
+===================
+100 numpy exercises
+===================
+
+A joint effort of the numpy community
+-------------------------------------
+
+The goal is both to offer a quick reference for new and old users and to
+provide also a set of exercices for those who teach. If you remember having
+asked or answered a (short) problem, you can send a pull request. The format
+is::
+
+ #. Find indices of non-zero elements from [1,2,0,0,4,0]
+
+    .. code:: python
+
+       # Author: Somebody
+
+       print np.nonzero([1,2,0,0,4,0])
+
+
+Here is what the page looks like so far:
+http://www.loria.fr/~rougier/teaching/numpy.100/index.html
+
+
+.. Note:: The level names came from an old-game (Dungeon Master)
+
+
+Repository is at: https://github.com/rougier/numpy-100
+
+
+**Contents**
+
+.. contents::
+   :local:
+   :depth: 1
+
+
+Neophyte
+========
+
+1. Import the numpy package under the name ``np``
+
+   .. code:: python
+
+      import numpy as np
+
+
+#. Print the numpy version and the configuration.
+
+   .. code:: python
+
+      print np.__version__
+      np.__config__.show()
+
+
+#. Create a null vector of size 10
+
+   .. code:: python
+
+      Z = np.zeros(10)
+
+#. Create a null vector of size 10 but the fifth value which is 1
+
+   .. code:: python
+
+      Z = np.zeros(10)
+      Z[4] = 1
+
+#. Create a vector with values ranging from 10 to 99
+
+   .. code:: python
+
+      Z = np.arange(10,100)
+
+#. Create a 3x3 matrix with values ranging from 0 to 8
+
+   .. code:: python
+
+      Z = np.arange(9).reshape(3,3)
+
+#. Find indices of non-zero elements from [1,2,0,0,4,0]
+
+   .. code:: python
+
+      nz = np.nonzero([1,2,0,0,4,0])
+
+
+#. Declare a 3x3 identity matrix
+
+   .. code:: python
+
+      Z = np.eye(3)
+
+#. Declare a 5x5 matrix with values 1,2,3,4 just below the diagonal
+
+   .. code:: python
+
+      Z = np.diag(1+np.arange(4),k=-1)
+
+
+#. Declare a 10x10x10 array with random values
+
+   .. code:: python
+
+      Z = np.random.random((10,10,10))
+
+Novice
+======
+
+#. Declare a 8x8 matrix and fill it with a checkerboard pattern
+
+   .. code:: python
+
+      Z = np.zeros((8,8))
+      Z[1::2,::2] = 1
+      Z[::2,1::2] = 1
+
+#. Declare a 10x10 array with random values and find the minimum and maximum values
+
+   .. code:: python
+
+      Z = np.random.random((10,10))
+      Zmin, Zmax = Z.min(), Z.max()
+
+#. Create a checkerboard 8x8 matrix using the tile function
+
+   .. code:: python
+
+      Z = np.tile( np.array([[0,1],[1,0]]), (4,4))
+
+#. Normalize a 5x5 random matrix (between 0 and 1)
+
+   .. code:: python
+
+      Z = np.random.random((5,5))
+      Zmax,Zmin = Z.max(), Z.min()
+      Z = (Z - Zmin)/(Zmax - Zmin)
+
+
+#. Multiply a 5x3 matrix by a 3x2 matrix (real matrix product)
+
+   .. code:: python
+
+      Z = np.dot(np.ones((5,3)), np.ones((3,2)))
+
+
+#. Create a 10x10 matrix with row values ranging from 0 to 9
+
+   .. code:: python
+
+    Z = np.zeros((10,10))
+    Z += np.arange(10)
+
+#. Create a vector of size 1000 with values ranging from 0 to 1, both excluded
+
+   .. code:: python
+
+    Z = np.random.linspace(0,1,1002,endpoint=True)[1:-1]
+
+#. Create a random vector of size 100 and sort it
+
+   .. code:: python
+
+    Z = np.random.random(100)
+    Z.sort()
+
+#. Consider two random matrices A anb B, check if they are equal.
+
+   .. code:: python
+
+      A = np.random.randint(0,2,(2,2))
+      B = np.random.randint(0,2,(2,2))
+      equal = np.allclose(A,B)
+
+#. Create a random vector of size 1000 and find the mean value
+
+   .. code:: python
+
+      Z = np.random.random(1000)
+      m = Z.mean()
+
+
+
+Apprentice
+==========
+
+
+#. Make an array immutable
+
+   .. code:: python
+
+      Z = np.zeros(10)
+      Z.flags.writeable = False
+
+
+#. Consider a random 100x2 matrix representing cartesian coordinates, convert
+   them to polar coordinates
+
+   .. code:: python
+
+      Z = np.random.random((100,2))
+      X,Y = Z[:,0], Z[:,1]
+      R = np.sqrt(X**2+Y**2)
+      T = np.arctan2(Y,X)
+
+
+#. Create random vector of size 100 and replace the maximum value by 0
+
+   .. code:: python
+
+    Z = np.random.random(100)
+    Z[Z.argmax()] = 0
+
+
+#. Declare a structured array with ``x`` and ``y`` coordinates covering the
+   [0,1]x[0,1] area.
+
+   .. code:: python
+
+      Z = np.zeros((10,10), [('x',float),('y',float)])
+      Z['x'], Z['y'] = np.meshgrid(np.linspace(0,1,10),
+                                   np.linspace(0,1,10))
+
+#. Print the minimum and maximum representable value for each numpy scalar type
+
+   .. code:: python
+
+      for dtype in [np.int8, np.int32, np.int64]:
+         print np.iinfo(dtype).min
+         print np.iinfo(dtype).max
+      for dtype in [np.float32, np.float64]:
+         print np.finfo(dtype).min
+         print np.finfo(dtype).max
+         print np.finfo(dtype).eps
+
+
+#. Create a structured array representing a position (x,y) and a color (r,g,b)
+
+   .. code:: python
+
+      Z = np.zeros(10, [ ('position', [ ('x', float, 1),
+                                        ('y', float, 1)]),
+                         ('color',    [ ('r', float, 1),
+                                        ('g', float, 1),
+                                        ('b', float, 1)])])
+
+
+#. Consider a random vector with shape (100,2) representing coordinates, find
+   point by point distances
+
+   .. code:: python
+
+      Z = np.random.random((10,2))
+      X,Y = np.atleast_2d(Z[:,0]), np.atleast_2d(Z[:,1])
+      D = np.sqrt( (X-X.T)**2 + (Y-Y.T)**2)
+
+      # Much faster with scipy
+      Z = np.random.random((10,2))
+      D = scipy.spatial.distance.cdist(Z,Z)
+
+
+
+#. Generate a generic 2D Gaussian-like array
+
+   .. code:: python
+
+      X, Y = np.meshgrid(np.linspace(-1,1,100), np.linspace(-1,1,100))
+      D = np.sqrt(X*X+Y*Y)
+      sigma, mu = 1.0, 0.0
+      G = np.exp(-( (D-mu)**2 / ( 2.0 * sigma**2 ) ) )
+
+#. Consider the vector [1, 2, 3, 4, 5], how to build a new vector with 3
+   consecutive zeros interleaved between each value ?
+
+   .. code:: python
+
+      # Author: Warren Weckesser
+
+      Z = np.array([1,2,3,4,5])
+      nz = 3
+      Z0 = np.zeros(len(Z) + (len(Z)-1)*(nz))
+      Z0[::nz+1] = Z
+
+
+#. Find the nearest value from a given value in an array
+
+   .. code:: python
+
+      Z.flat[np.abs(Z - z).argmin()]
+
+
+
+Journeyman
+==========
+
+#. Consider the following file::
+
+    1,2,3,4,5
+    6,,,7,8
+    ,,9,10,11
+
+   How to read it ?
+
+   .. code:: python
+
+      Z = genfromtxt("missing.dat", delimiter=",")
+
+
+#. Consider a generator function that generates 10 integers and use it to build an
+   array
+
+   .. code:: python
+
+      def generate():
+          for x in xrange(10):
+              yield x
+      Z = np.fromiter(generate(),dtype=float,count=-1)
+
+
+#. Consider a given vector, how to add 1 to each element indexed by a second
+   vector (be careful with repeated indices) ?
+
+   .. code:: python
+
+      # Author: Brett Olsen
+
+      Z = np.ones(10)
+      I = np.random.randint(0,len(Z),20)
+      Z += np.bincount(I, minlength=len(Z))
+
+
+#. How to accumulate elements of a vector (X) to an array (F) based on an index
+   list (I) ?
+
+   .. code:: python
+
+      # Author: Alan G Isaac
+
+      X = [1,2,3,4,5,6]
+      I = [1,3,9,3,4,1]
+      F = np.bincount(I,X)
+
+#. Considering a (w,h,3) image of (dtype=ubyte), compute the number of unique
+   colors
+
+   .. code:: python
+
+      # Author: Nadav Horesh
+
+      w,h = 16,16
+      I = np.random.randint(0,2,(h,w,3)).astype(np.ubyte)
+      F = I[...,0]*256*256 + I[...,1]*256 +I[...,2]
+      n = len(np.unique(F))
+
+      np.unique(I)
+
+#. Considering a four dimensions array, how to get sum over the last two axis at once ?
+
+
+   .. code:: python
+
+      A = np.random.randint(0,10,(3,4,3,4))
+      sum = A.reshape(A.shape[:-2] + (-1,)).sum(axis=-1)
+
+
+
+Craftsman
+=========
+
+#. Consider a one-dimensional array Z, build a two-dimensional array whose
+   first row is (Z[0],Z[1],Z[2]) and each subsequent row is shifted by 1 (last
+   row should be (Z[-3],Z[-2],Z[-1])
+
+   .. code:: python
+
+      # Author: Joe Kington / Erik Rigtorp
+
+      def rolling(a, window):
+          shape = (a.size - window + 1, window)
+          strides = (a.itemsize, a.itemsize)
+          return np.lib.stride_tricks.as_strided(a, shape=shape, strides=strides)
+
+      Z = rolling(np.arange(100), 3)
+
+#. Consider a set of 100 triplets describing 100 triangles (with shared
+   vertices), find the set of unique line segments composing all the triangles.
+
+   .. code:: python
+
+      # Author: Nicolas Rougier
+
+      faces = np.random.randint(0,100,(100,3))
+
+      F = np.roll(faces.repeat(2,axis=1),-1,axis=1)
+      F = F.reshape(len(F)*3,2)
+      F = np.sort(F,axis=1)
+      G = F.view( dtype=[('p0',F.dtype),('p1',F.dtype)] )
+      G = np.unique(G)
+
+
+
+Artisan
+=======
+
+#. Considering a 100x3 matrix, extract rows with unequal values (e.g. [2,2,3])
+
+   .. code:: python
+
+      # Author: Robert Kern
+
+      Z = np.random.randint(0,5,(100,3))
+      E = np.logical_and.reduce(Z[:,1:] == Z[:,:-1], axis=1)
+      U = Z[~E]
+
+#. Convert a vector of ints into a matrix binary representation.
+
+   .. code:: python
+
+      # Author: Warren Weckesser
+
+      I = np.array([0, 1, 2, 3, 15, 16, 32, 64, 128])
+      B = ((I.reshape(-1,1) & (2**np.arange(8))) != 0).astype(int)
+      B = B[:,::-1]
+
+      # Author: Daniel T. McDonald
+
+      I = np.array([0, 1, 2, 3, 15, 16, 32, 64, 128], dtype=np.uint8)
+      np.unpackbits(I[:, np.newaxis], axis=1)
+
+
+
+Adept
+=====
+
+#. Consider an arbitrary array, write a function that extract a subpart with a
+   fixed shape and centered on a given element (pad with a ``fill`` value when
+   necessary)
+
+   .. code :: python
+
+      # Author: Nicolas Rougier
+
+      Z = np.random.random((25,25))
+      shape = (3,3)
+      fill  = 0
+      position = (0,0)
+
+      R = np.ones(shape, dtype=Z.dtype)*fill
+      P  = np.array(list(position)).astype(int)
+      Rs = np.array(list(R.shape)).astype(int)
+      Zs = np.array(list(Z.shape)).astype(int)
+
+      R_start = np.zeros((len(shape),)).astype(int)
+      R_stop  = np.array(list(shape)).astype(int)
+      Z_start = (P-Rs//2)
+      Z_stop  = (P+Rs//2)+Rs%2
+
+      R_start = (R_start - np.minimum(Z_start,0)).tolist()
+      Z_start = (np.maximum(Z_start,0)).tolist()
+      R_stop = np.maximum(R_start, (R_stop - np.maximum(Z_stop-Zs,0))).tolist()
+      Z_stop = (np.minimum(Z_stop,Zs)).tolist()
+
+      r = [slice(start,stop) for start,stop in zip(R_start,R_stop)]
+      z = [slice(start,stop) for start,stop in zip(Z_start,Z_stop)]
+      R[r] = Z[z]
+
+
+
+
+
+
+Expert
+======
+
+#. 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 ?
+
+   .. code:: python
+
+      # Author: Gabe Schwartz
+
+      A = np.random.randint(0,5,(8,3))
+      B = np.random.randint(0,5,(2,2))
+
+      C = (A[..., np.newaxis, np.newaxis] == B)
+      rows = (C.sum(axis=(1,2,3)) >= B.shape[1]).nonzero()[0]
+
+
+#. Extract all the contiguous 3x3 blocks from a random 10x10 matrix.
+
+   .. code:: python
+
+      Z = np.random.randint(0,5,(10,10))
+      n = 3
+      i = 1 + (Z.shape[0]-3)
+      j = 1 + (Z.shape[1]-3)
+      C = stride_tricks.as_strided(Z, shape=(i, j, n, n), strides=Z.strides + Z.strides)
+
+
+Master
+======
+
+Archmaster
+==========
diff --git a/README.txt b/README.txt
deleted file mode 100644
index 3562846..0000000
--- a/README.txt
+++ /dev/null
@@ -1,26 +0,0 @@
-100 Numpy exercices
-===================
-
-The goal is both to offer a quick reference for new and old users and to
-provide also a set of exercices for those who teach.
-
-If you remember having asked or answered a (short) problem, you can send a pull
-request. The format is:
-
-
-#. Find indices of non-zero elements from [1,2,0,0,4,0]
-
-   .. code:: python
-
-      # Author: Somebody
-
-      print np.nonzero([1,2,0,0,4,0])
-
-
-If you can provide the assumed level of the answer, that would be even better.
-
-Here is what the page looks like so far:
-
-http://www.loria.fr/~rougier/teaching/numpy.100/index.html
-
-(The level names came from an old-game: Dungeon Master)