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class="documentwrapper"> <div class="bodywrapper"> <div class="body"> <div class="section" id="confusion-matrix"> <span id="example-plot-confusion-matrix-py"></span><h1>Confusion matrix<a class="headerlink" href="#confusion-matrix" title="Permalink to this headline">ΒΆ</a></h1> <p>Example of confusion matrix usage to evaluate the quality of the output of a classifier.</p> <img alt="auto_examples/images/plot_confusion_matrix.png" class="align-center" src="auto_examples/images/plot_confusion_matrix.png" /> <p><strong>Python source code:</strong> <a class="reference download internal" href="../_downloads/plot_confusion_matrix.py"><tt class="xref download docutils literal"><span class="pre">plot_confusion_matrix.py</span></tt></a></p> <div class="highlight-python"><div class="highlight"><pre><span class="k">print</span> <span class="n">__doc__</span> <span class="kn">import</span> <span class="nn">random</span> <span class="kn">import</span> <span class="nn">pylab</span> <span class="kn">as</span> <span class="nn">pl</span> <span class="kn">from</span> <span class="nn">scikits.learn</span> <span class="kn">import</span> <span class="n">svm</span><span class="p">,</span> <span class="n">datasets</span> <span class="kn">from</span> <span class="nn">scikits.learn.metrics</span> <span class="kn">import</span> <span class="n">confusion_matrix</span> <span class="c"># import some data to play with</span> <span class="n">iris</span> <span class="o">=</span> <span class="n">datasets</span><span class="o">.</span><span class="n">load_iris</span><span class="p">()</span> <span class="n">X</span> <span class="o">=</span> <span class="n">iris</span><span class="o">.</span><span class="n">data</span> <span class="n">y</span> <span class="o">=</span> <span class="n">iris</span><span class="o">.</span><span class="n">target</span> <span class="n">n_samples</span><span class="p">,</span> <span class="n">n_features</span> <span class="o">=</span> <span class="n">X</span><span class="o">.</span><span class="n">shape</span> <span class="n">p</span> <span class="o">=</span> <span class="nb">range</span><span class="p">(</span><span class="n">n_samples</span><span class="p">)</span> <span class="n">random</span><span class="o">.</span><span class="n">seed</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span> <span class="n">random</span><span class="o">.</span><span class="n">shuffle</span><span class="p">(</span><span class="n">p</span><span class="p">)</span> <span class="n">X</span><span class="p">,</span> <span class="n">y</span> <span class="o">=</span> <span class="n">X</span><span class="p">[</span><span class="n">p</span><span class="p">],</span> <span class="n">y</span><span class="p">[</span><span class="n">p</span><span class="p">]</span> <span class="n">half</span> <span class="o">=</span> <span class="nb">int</span><span class="p">(</span><span class="n">n_samples</span><span class="o">/</span><span class="mi">2</span><span class="p">)</span> <span class="c"># Run classifier</span> <span class="n">classifier</span> <span class="o">=</span> <span class="n">svm</span><span class="o">.</span><span class="n">SVC</span><span class="p">(</span><span class="n">kernel</span><span class="o">=</span><span class="s">'linear'</span><span class="p">)</span> <span class="n">y_</span> <span class="o">=</span> <span class="n">classifier</span><span class="o">.</span><span class="n">fit</span><span class="p">(</span><span class="n">X</span><span class="p">[:</span><span class="n">half</span><span class="p">],</span><span class="n">y</span><span class="p">[:</span><span class="n">half</span><span class="p">])</span><span class="o">.</span><span class="n">predict</span><span class="p">(</span><span class="n">X</span><span class="p">[</span><span class="n">half</span><span class="p">:])</span> <span class="c"># Compute confusion matrix</span> <span class="n">cm</span> <span class="o">=</span> <span class="n">confusion_matrix</span><span class="p">(</span><span class="n">y</span><span class="p">[</span><span class="n">half</span><span class="p">:],</span> <span class="n">y_</span><span class="p">)</span> <span class="k">print</span> <span class="n">cm</span> <span class="c"># Show confusion matrix</span> <span class="n">pl</span><span class="o">.</span><span class="n">matshow</span><span class="p">(</span><span class="n">cm</span><span class="p">)</span> <span class="n">pl</span><span class="o">.</span><span class="n">title</span><span class="p">(</span><span class="s">'Confusion matrix'</span><span class="p">)</span> <span class="n">pl</span><span class="o">.</span><span class="n">colorbar</span><span class="p">()</span> <span class="n">pl</span><span class="o">.</span><span class="n">show</span><span class="p">()</span> </pre></div> </div> </div> </div> </div> </div> <div class="clearer"></div> </div> </div> <div class="footer"> <p style="text-align: center">This documentation 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