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<div class="section" id="api-example-code-collections-demo-py">
<span id="api-collections-demo"></span><h1>api example code: collections_demo.py<a class="headerlink" href="#api-example-code-collections-demo-py" title="Permalink to this headline">ΒΆ</a></h1>
<p>(<a class="reference external" href="../../mpl_examples/api/collections_demo.py">Source code</a>)</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c">#!/usr/bin/env python</span>
<span class="sd">'''Demonstration of LineCollection, PolyCollection, and</span>
<span class="sd">RegularPolyCollection with autoscaling.</span>
<span class="sd">For the first two subplots, we will use spirals. Their</span>
<span class="sd">size will be set in plot units, not data units. Their positions</span>
<span class="sd">will be set in data units by using the "offsets" and "transOffset"</span>
<span class="sd">kwargs of the LineCollection and PolyCollection.</span>
<span class="sd">The third subplot will make regular polygons, with the same</span>
<span class="sd">type of scaling and positioning as in the first two.</span>
<span class="sd">The last subplot illustrates the use of "offsets=(xo,yo)",</span>
<span class="sd">that is, a single tuple instead of a list of tuples, to generate</span>
<span class="sd">successively offset curves, with the offset given in data</span>
<span class="sd">units. This behavior is available only for the LineCollection.</span>
<span class="sd">'''</span>
<span class="kn">import</span> <span class="nn">matplotlib.pyplot</span> <span class="kn">as</span> <span class="nn">plt</span>
<span class="kn">from</span> <span class="nn">matplotlib</span> <span class="kn">import</span> <span class="n">collections</span><span class="p">,</span> <span class="n">transforms</span>
<span class="kn">from</span> <span class="nn">matplotlib.colors</span> <span class="kn">import</span> <span class="n">colorConverter</span>
<span class="kn">import</span> <span class="nn">numpy</span> <span class="kn">as</span> <span class="nn">np</span>
<span class="n">nverts</span> <span class="o">=</span> <span class="mi">50</span>
<span class="n">npts</span> <span class="o">=</span> <span class="mi">100</span>
<span class="c"># Make some spirals</span>
<span class="n">r</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">array</span><span class="p">(</span><span class="nb">range</span><span class="p">(</span><span class="n">nverts</span><span class="p">))</span>
<span class="n">theta</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">array</span><span class="p">(</span><span class="nb">range</span><span class="p">(</span><span class="n">nverts</span><span class="p">))</span> <span class="o">*</span> <span class="p">(</span><span class="mi">2</span><span class="o">*</span><span class="n">np</span><span class="o">.</span><span class="n">pi</span><span class="p">)</span><span class="o">/</span><span class="p">(</span><span class="n">nverts</span><span class="o">-</span><span class="mi">1</span><span class="p">)</span>
<span class="n">xx</span> <span class="o">=</span> <span class="n">r</span> <span class="o">*</span> <span class="n">np</span><span class="o">.</span><span class="n">sin</span><span class="p">(</span><span class="n">theta</span><span class="p">)</span>
<span class="n">yy</span> <span class="o">=</span> <span class="n">r</span> <span class="o">*</span> <span class="n">np</span><span class="o">.</span><span class="n">cos</span><span class="p">(</span><span class="n">theta</span><span class="p">)</span>
<span class="n">spiral</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="nb">zip</span><span class="p">(</span><span class="n">xx</span><span class="p">,</span><span class="n">yy</span><span class="p">))</span>
<span class="c"># Make some offsets</span>
<span class="n">rs</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">RandomState</span><span class="p">([</span><span class="mi">12345678</span><span class="p">])</span>
<span class="n">xo</span> <span class="o">=</span> <span class="n">rs</span><span class="o">.</span><span class="n">randn</span><span class="p">(</span><span class="n">npts</span><span class="p">)</span>
<span class="n">yo</span> <span class="o">=</span> <span class="n">rs</span><span class="o">.</span><span class="n">randn</span><span class="p">(</span><span class="n">npts</span><span class="p">)</span>
<span class="n">xyo</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="nb">zip</span><span class="p">(</span><span class="n">xo</span><span class="p">,</span> <span class="n">yo</span><span class="p">))</span>
<span class="c"># Make a list of colors cycling through the rgbcmyk series.</span>
<span class="n">colors</span> <span class="o">=</span> <span class="p">[</span><span class="n">colorConverter</span><span class="o">.</span><span class="n">to_rgba</span><span class="p">(</span><span class="n">c</span><span class="p">)</span> <span class="k">for</span> <span class="n">c</span> <span class="ow">in</span> <span class="p">(</span><span class="s">'r'</span><span class="p">,</span><span class="s">'g'</span><span class="p">,</span><span class="s">'b'</span><span class="p">,</span><span class="s">'c'</span><span class="p">,</span><span class="s">'y'</span><span class="p">,</span><span class="s">'m'</span><span class="p">,</span><span class="s">'k'</span><span class="p">)]</span>
<span class="n">fig</span> <span class="o">=</span> <span class="n">plt</span><span class="o">.</span><span class="n">figure</span><span class="p">()</span>
<span class="n">a</span> <span class="o">=</span> <span class="n">fig</span><span class="o">.</span><span class="n">add_subplot</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">)</span>
<span class="n">col</span> <span class="o">=</span> <span class="n">collections</span><span class="o">.</span><span class="n">LineCollection</span><span class="p">([</span><span class="n">spiral</span><span class="p">],</span> <span class="n">offsets</span><span class="o">=</span><span class="n">xyo</span><span class="p">,</span>
<span class="n">transOffset</span><span class="o">=</span><span class="n">a</span><span class="o">.</span><span class="n">transData</span><span class="p">)</span>
<span class="n">trans</span> <span class="o">=</span> <span class="n">fig</span><span class="o">.</span><span class="n">dpi_scale_trans</span> <span class="o">+</span> <span class="n">transforms</span><span class="o">.</span><span class="n">Affine2D</span><span class="p">()</span><span class="o">.</span><span class="n">scale</span><span class="p">(</span><span class="mf">1.0</span><span class="o">/</span><span class="mf">72.0</span><span class="p">)</span>
<span class="n">col</span><span class="o">.</span><span class="n">set_transform</span><span class="p">(</span><span class="n">trans</span><span class="p">)</span> <span class="c"># the points to pixels transform</span>
<span class="c"># Note: the first argument to the collection initializer</span>
<span class="c"># must be a list of sequences of x,y tuples; we have only</span>
<span class="c"># one sequence, but we still have to put it in a list.</span>
<span class="n">a</span><span class="o">.</span><span class="n">add_collection</span><span class="p">(</span><span class="n">col</span><span class="p">,</span> <span class="n">autolim</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
<span class="c"># autolim=True enables autoscaling. For collections with</span>
<span class="c"># offsets like this, it is neither efficient nor accurate,</span>
<span class="c"># but it is good enough to generate a plot that you can use</span>
<span class="c"># as a starting point. If you know beforehand the range of</span>
<span class="c"># x and y that you want to show, it is better to set them</span>
<span class="c"># explicitly, leave out the autolim kwarg (or set it to False),</span>
<span class="c"># and omit the 'a.autoscale_view()' call below.</span>
<span class="c"># Make a transform for the line segments such that their size is</span>
<span class="c"># given in points:</span>
<span class="n">col</span><span class="o">.</span><span class="n">set_color</span><span class="p">(</span><span class="n">colors</span><span class="p">)</span>
<span class="n">a</span><span class="o">.</span><span class="n">autoscale_view</span><span class="p">()</span> <span class="c"># See comment above, after a.add_collection.</span>
<span class="n">a</span><span class="o">.</span><span class="n">set_title</span><span class="p">(</span><span class="s">'LineCollection using offsets'</span><span class="p">)</span>
<span class="c"># The same data as above, but fill the curves.</span>
<span class="n">a</span> <span class="o">=</span> <span class="n">fig</span><span class="o">.</span><span class="n">add_subplot</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">2</span><span class="p">)</span>
<span class="n">col</span> <span class="o">=</span> <span class="n">collections</span><span class="o">.</span><span class="n">PolyCollection</span><span class="p">([</span><span class="n">spiral</span><span class="p">],</span> <span class="n">offsets</span><span class="o">=</span><span class="n">xyo</span><span class="p">,</span>
<span class="n">transOffset</span><span class="o">=</span><span class="n">a</span><span class="o">.</span><span class="n">transData</span><span class="p">)</span>
<span class="n">trans</span> <span class="o">=</span> <span class="n">transforms</span><span class="o">.</span><span class="n">Affine2D</span><span class="p">()</span><span class="o">.</span><span class="n">scale</span><span class="p">(</span><span class="n">fig</span><span class="o">.</span><span class="n">dpi</span><span class="o">/</span><span class="mf">72.0</span><span class="p">)</span>
<span class="n">col</span><span class="o">.</span><span class="n">set_transform</span><span class="p">(</span><span class="n">trans</span><span class="p">)</span> <span class="c"># the points to pixels transform</span>
<span class="n">a</span><span class="o">.</span><span class="n">add_collection</span><span class="p">(</span><span class="n">col</span><span class="p">,</span> <span class="n">autolim</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
<span class="n">col</span><span class="o">.</span><span class="n">set_color</span><span class="p">(</span><span class="n">colors</span><span class="p">)</span>
<span class="n">a</span><span class="o">.</span><span class="n">autoscale_view</span><span class="p">()</span>
<span class="n">a</span><span class="o">.</span><span class="n">set_title</span><span class="p">(</span><span class="s">'PolyCollection using offsets'</span><span class="p">)</span>
<span class="c"># 7-sided regular polygons</span>
<span class="n">a</span> <span class="o">=</span> <span class="n">fig</span><span class="o">.</span><span class="n">add_subplot</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">)</span>
<span class="n">col</span> <span class="o">=</span> <span class="n">collections</span><span class="o">.</span><span class="n">RegularPolyCollection</span><span class="p">(</span><span class="mi">7</span><span class="p">,</span>
<span class="n">sizes</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">fabs</span><span class="p">(</span><span class="n">xx</span><span class="p">)</span><span class="o">*</span><span class="mf">10.0</span><span class="p">,</span> <span class="n">offsets</span><span class="o">=</span><span class="n">xyo</span><span class="p">,</span>
<span class="n">transOffset</span><span class="o">=</span><span class="n">a</span><span class="o">.</span><span class="n">transData</span><span class="p">)</span>
<span class="n">trans</span> <span class="o">=</span> <span class="n">transforms</span><span class="o">.</span><span class="n">Affine2D</span><span class="p">()</span><span class="o">.</span><span class="n">scale</span><span class="p">(</span><span class="n">fig</span><span class="o">.</span><span class="n">dpi</span><span class="o">/</span><span class="mf">72.0</span><span class="p">)</span>
<span class="n">col</span><span class="o">.</span><span class="n">set_transform</span><span class="p">(</span><span class="n">trans</span><span class="p">)</span> <span class="c"># the points to pixels transform</span>
<span class="n">a</span><span class="o">.</span><span class="n">add_collection</span><span class="p">(</span><span class="n">col</span><span class="p">,</span> <span class="n">autolim</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
<span class="n">col</span><span class="o">.</span><span class="n">set_color</span><span class="p">(</span><span class="n">colors</span><span class="p">)</span>
<span class="n">a</span><span class="o">.</span><span class="n">autoscale_view</span><span class="p">()</span>
<span class="n">a</span><span class="o">.</span><span class="n">set_title</span><span class="p">(</span><span class="s">'RegularPolyCollection using offsets'</span><span class="p">)</span>
<span class="c"># Simulate a series of ocean current profiles, successively</span>
<span class="c"># offset by 0.1 m/s so that they form what is sometimes called</span>
<span class="c"># a "waterfall" plot or a "stagger" plot.</span>
<span class="n">a</span> <span class="o">=</span> <span class="n">fig</span><span class="o">.</span><span class="n">add_subplot</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">)</span>
<span class="n">nverts</span> <span class="o">=</span> <span class="mi">60</span>
<span class="n">ncurves</span> <span class="o">=</span> <span class="mi">20</span>
<span class="n">offs</span> <span class="o">=</span> <span class="p">(</span><span class="mf">0.1</span><span class="p">,</span> <span class="mf">0.0</span><span class="p">)</span>
<span class="n">yy</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">linspace</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">2</span><span class="o">*</span><span class="n">np</span><span class="o">.</span><span class="n">pi</span><span class="p">,</span> <span class="n">nverts</span><span class="p">)</span>
<span class="n">ym</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">amax</span><span class="p">(</span><span class="n">yy</span><span class="p">)</span>
<span class="n">xx</span> <span class="o">=</span> <span class="p">(</span><span class="mf">0.2</span> <span class="o">+</span> <span class="p">(</span><span class="n">ym</span><span class="o">-</span><span class="n">yy</span><span class="p">)</span><span class="o">/</span><span class="n">ym</span><span class="p">)</span><span class="o">**</span><span class="mi">2</span> <span class="o">*</span> <span class="n">np</span><span class="o">.</span><span class="n">cos</span><span class="p">(</span><span class="n">yy</span><span class="o">-</span><span class="mf">0.4</span><span class="p">)</span> <span class="o">*</span> <span class="mf">0.5</span>
<span class="n">segs</span> <span class="o">=</span> <span class="p">[]</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="n">ncurves</span><span class="p">):</span>
<span class="n">xxx</span> <span class="o">=</span> <span class="n">xx</span> <span class="o">+</span> <span class="mf">0.02</span><span class="o">*</span><span class="n">rs</span><span class="o">.</span><span class="n">randn</span><span class="p">(</span><span class="n">nverts</span><span class="p">)</span>
<span class="n">curve</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="nb">zip</span><span class="p">(</span><span class="n">xxx</span><span class="p">,</span> <span class="n">yy</span><span class="o">*</span><span class="mi">100</span><span class="p">))</span>
<span class="n">segs</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">curve</span><span class="p">)</span>
<span class="n">col</span> <span class="o">=</span> <span class="n">collections</span><span class="o">.</span><span class="n">LineCollection</span><span class="p">(</span><span class="n">segs</span><span class="p">,</span> <span class="n">offsets</span><span class="o">=</span><span class="n">offs</span><span class="p">)</span>
<span class="n">a</span><span class="o">.</span><span class="n">add_collection</span><span class="p">(</span><span class="n">col</span><span class="p">,</span> <span class="n">autolim</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
<span class="n">col</span><span class="o">.</span><span class="n">set_color</span><span class="p">(</span><span class="n">colors</span><span class="p">)</span>
<span class="n">a</span><span class="o">.</span><span class="n">autoscale_view</span><span class="p">()</span>
<span class="n">a</span><span class="o">.</span><span class="n">set_title</span><span class="p">(</span><span class="s">'Successive data offsets'</span><span class="p">)</span>
<span class="n">a</span><span class="o">.</span><span class="n">set_xlabel</span><span class="p">(</span><span class="s">'Zonal velocity component (m/s)'</span><span class="p">)</span>
<span class="n">a</span><span class="o">.</span><span class="n">set_ylabel</span><span class="p">(</span><span class="s">'Depth (m)'</span><span class="p">)</span>
<span class="c"># Reverse the y-axis so depth increases downward</span>
<span class="n">a</span><span class="o">.</span><span class="n">set_ylim</span><span class="p">(</span><span class="n">a</span><span class="o">.</span><span class="n">get_ylim</span><span class="p">()[::</span><span class="o">-</span><span class="mi">1</span><span class="p">])</span>
<span class="n">plt</span><span class="o">.</span><span class="n">show</span><span class="p">()</span>
</pre></div>
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