1 2 3 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 4 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 5 <html xmlns="http://www.w3.org/1999/xhtml"> 6 <head> 7 <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 8 9 <title>A simple tutorial on Arrays - Boost.Python NumPy extension 1.0 documentation</title> 10 <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> 11 <link rel="stylesheet" href="../_static/style.css" type="text/css" /> 12 <script type="text/javascript"> 13 var DOCUMENTATION_OPTIONS = { 14 URL_ROOT: '../', 15 VERSION: '1.0', 16 COLLAPSE_MODINDEX: false, 17 FILE_SUFFIX: '.html' 18 }; 19 </script> 20 <script type="text/javascript" src="../_static/jquery.js"></script> 21 <script type="text/javascript" src="../_static/underscore.js"></script> 22 <script type="text/javascript" src="../_static/doctools.js"></script> 23 <link rel="index" title="Index" href="../genindex.html" /> 24 <link rel="search" title="Search" href="../search.html" /> 25 <link rel="top" title="Boost.Python NumPy extension 1.0 documentation" href="../index.html" /> 26 <link rel="up" title="Boost.Python NumPy extension Tutorial" href="index.html" /> 27 <link rel="next" title="How to use dtypes" href="dtype.html" /> 28 <link rel="prev" title="Boost.Python NumPy extension Tutorial" href="index.html" /> 29 </head> 30 <body> 31 <div class="header"> 32 <table border="0" cellpadding="7" cellspacing="0" width="100%" summary= 33 "header"> 34 <tr> 35 <td valign="top" width="300"> 36 <h3><a href="../index.html"><img 37 alt="C++ Boost" src="../_static/bpl.png" border="0"></a></h3> 38 </td> 39 40 <td > 41 <h1 align="center"><a href="../index.html">(NumPy)</a></h1> 42 <!-- <h2 align="center">CallPolicies Concept</h2>--> 43 </td> 44 <td> 45 <div id="searchbox" style="display: none"> 46 <form class="search" action="../search.html" method="get"> 47 <input type="text" name="q" size="18" /> 48 <input type="submit" value="Search" /> 49 <input type="hidden" name="check_keywords" value="yes" /> 50 <input type="hidden" name="area" value="default" /> 51 </form> 52 </div> 53 <script type="text/javascript">$('#searchbox').show(0);</script> 54 </td> 55 </tr> 56 </table> 57 </div> 58 <hr/> 59 <div class="content"> 60 <div class="navbar" style="text-align:right;"> 61 62 63 <a class="prev" title="Boost.Python NumPy extension Tutorial" href="index.html"><img src="../_static/prev.png" alt="prev"/></a> 64 <a class="up" title="Boost.Python NumPy extension Tutorial" href="index.html"><img src="../_static/up.png" alt="up"/></a> 65 <a class="next" title="How to use dtypes" href="dtype.html"><img src="../_static/next.png" alt="next"/></a> 66 67 </div> 68 69 <div class="section" id="a-simple-tutorial-on-arrays"> 70 <h1>A simple tutorial on Arrays</h1> 71 <p>Let’s start with a simple tutorial to create and modify arrays.</p> 72 <p>Get the necessary headers for numpy components and set up necessary namespaces:</p> 73 <div class="highlight-c++"><div class="highlight"><pre><span class="cp">#include</span> <span class="cpf"><boost/python/numpy.hpp></span><span class="cp"></span> 74 <span class="cp">#include</span> <span class="cpf"><iostream></span><span class="cp"></span> 75 76 <span class="k">namespace</span> <span class="n">p</span> <span class="o">=</span> <span class="n">boost</span><span class="o">::</span><span class="n">python</span><span class="p">;</span> 77 <span class="k">namespace</span> <span class="n">np</span> <span class="o">=</span> <span class="n">boost</span><span class="o">::</span><span class="n">python</span><span class="o">::</span><span class="n">numpy</span><span class="p">;</span> 78 </pre></div> 79 </div> 80 <p>Initialise the Python runtime, and the numpy module. Failure to call these results in segmentation errors:</p> 81 <div class="highlight-c++"><div class="highlight"><pre><span class="kt">int</span> <span class="nf">main</span><span class="p">(</span><span class="kt">int</span> <span class="n">argc</span><span class="p">,</span> <span class="kt">char</span> <span class="o">**</span><span class="n">argv</span><span class="p">)</span> 82 <span class="p">{</span> 83 <span class="n">Py_Initialize</span><span class="p">();</span> 84 <span class="n">np</span><span class="o">::</span><span class="n">initialize</span><span class="p">();</span> 85 </pre></div> 86 </div> 87 <p>Zero filled n-dimensional arrays can be created using the shape and data-type of the array as a parameter. Here, the shape is 3x3 and the datatype is the built-in float type:</p> 88 <div class="highlight-c++"><div class="highlight"><pre><span class="n">p</span><span class="o">::</span><span class="n">tuple</span> <span class="n">shape</span> <span class="o">=</span> <span class="n">p</span><span class="o">::</span><span class="n">make_tuple</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="mi">3</span><span class="p">);</span> 89 <span class="n">np</span><span class="o">::</span><span class="n">dtype</span> <span class="n">dtype</span> <span class="o">=</span> <span class="n">np</span><span class="o">::</span><span class="n">dtype</span><span class="o">::</span><span class="n">get_builtin</span><span class="o"><</span><span class="kt">float</span><span class="o">></span><span class="p">();</span> 90 <span class="n">np</span><span class="o">::</span><span class="n">ndarray</span> <span class="n">a</span> <span class="o">=</span> <span class="n">np</span><span class="o">::</span><span class="n">zeros</span><span class="p">(</span><span class="n">shape</span><span class="p">,</span> <span class="n">dtype</span><span class="p">);</span> 91 </pre></div> 92 </div> 93 <p>You can also create an empty array like this</p> 94 <div class="highlight-c++"><div class="highlight"><pre><span class="n">np</span><span class="o">::</span><span class="n">ndarray</span> <span class="n">b</span> <span class="o">=</span> <span class="n">np</span><span class="o">::</span><span class="n">empty</span><span class="p">(</span><span class="n">shape</span><span class="p">,</span><span class="n">dtype</span><span class="p">);</span> 95 </pre></div> 96 </div> 97 <p>Print the original and reshaped array. The array a which is a list is first converted to a string, and each value in the list is extracted using extract< >:</p> 98 <div class="highlight-c++"><div class="highlight"><pre> <span class="n">std</span><span class="o">::</span><span class="n">cout</span> <span class="o"><<</span> <span class="s">"Original array:</span><span class="se">\n</span><span class="s">"</span> <span class="o"><<</span> <span class="n">p</span><span class="o">::</span><span class="n">extract</span><span class="o"><</span><span class="kt">char</span> <span class="k">const</span> <span class="o">*></span><span class="p">(</span><span class="n">p</span><span class="o">::</span><span class="n">str</span><span class="p">(</span><span class="n">a</span><span class="p">))</span> <span class="o"><<</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> 99 100 <span class="c1">// Reshape the array into a 1D array</span> 101 <span class="n">a</span> <span class="o">=</span> <span class="n">a</span><span class="p">.</span><span class="n">reshape</span><span class="p">(</span><span class="n">p</span><span class="o">::</span><span class="n">make_tuple</span><span class="p">(</span><span class="mi">9</span><span class="p">));</span> 102 <span class="c1">// Print it again.</span> 103 <span class="n">std</span><span class="o">::</span><span class="n">cout</span> <span class="o"><<</span> <span class="s">"Reshaped array:</span><span class="se">\n</span><span class="s">"</span> <span class="o"><<</span> <span class="n">p</span><span class="o">::</span><span class="n">extract</span><span class="o"><</span><span class="kt">char</span> <span class="k">const</span> <span class="o">*></span><span class="p">(</span><span class="n">p</span><span class="o">::</span><span class="n">str</span><span class="p">(</span><span class="n">a</span><span class="p">))</span> <span class="o"><<</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> 104 <span class="p">}</span> 105 </pre></div> 106 </div> 107 </div> 108 109 110 <div class="navbar" style="text-align:right;"> 111 112 113 <a class="prev" title="Boost.Python NumPy extension Tutorial" href="index.html"><img src="../_static/prev.png" alt="prev"/></a> 114 <a class="up" title="Boost.Python NumPy extension Tutorial" href="index.html"><img src="../_static/up.png" alt="up"/></a> 115 <a class="next" title="How to use dtypes" href="dtype.html"><img src="../_static/next.png" alt="next"/></a> 116 117 </div> 118 </div> 119 </body> 120 </html>
