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<center><h1>Density chart with several groups</h1></center>
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<center><p style="max-width: 600px; margin-top: 40px">A <a href="https://www.data-to-viz.com/graph/density.html">density plot</a> is a representation of the distribution of a numeric variable. Comparing the distribution of several variables with density charts is possible. Here are a few examples with their <a href="ggplot2-package.html">ggplot2</a> implementation.</p></center>
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<a class="btn btn-secondary btn-xl text-uppercase js-scroll-trigger" href='density-plot.html'>Density Section</a>
<a class="btn btn-secondary btn-xl text-uppercase js-scroll-trigger" href='https://www.data-to-viz.com/story/OneNumOneCatSeveralObs.html'>Comparing distributions</a>
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<h1 id="multi-density-chart">Multi density chart</h1>
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<p>A multi density chart is a <a href="density-plot.html">density chart</a> where several groups are represented. It allows to compare their distribution. The issue with this kind of chart is that it gets easily <u>cluttered</u>: groups overlap each other and the figure gets unreadable.</p>
<p>An easy workaround is to use <u>transparency</u>. However, it won’t solve the issue completely and is is often better to consider the examples suggested further in this document.</p>
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<div class="sourceCode" id="cb1"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb1-1" data-line-number="1"><span class="co"># Libraries</span></a>
<a class="sourceLine" id="cb1-2" data-line-number="2"><span class="kw">library</span>(ggplot2)</a>
<a class="sourceLine" id="cb1-3" data-line-number="3"><span class="kw">library</span>(hrbrthemes)</a>
<a class="sourceLine" id="cb1-4" data-line-number="4"><span class="kw">library</span>(dplyr)</a>
<a class="sourceLine" id="cb1-5" data-line-number="5"><span class="kw">library</span>(tidyr)</a>
<a class="sourceLine" id="cb1-6" data-line-number="6"><span class="kw">library</span>(viridis)</a>
<a class="sourceLine" id="cb1-7" data-line-number="7"></a>
<a class="sourceLine" id="cb1-8" data-line-number="8"><span class="co"># The diamonds dataset is natively available with R.</span></a>
<a class="sourceLine" id="cb1-9" data-line-number="9"></a>
<a class="sourceLine" id="cb1-10" data-line-number="10"><span class="co"># Without transparency (left)</span></a>
<a class="sourceLine" id="cb1-11" data-line-number="11">p1 <-<span class="st"> </span><span class="kw">ggplot</span>(<span class="dt">data=</span>diamonds, <span class="kw">aes</span>(<span class="dt">x=</span>price, <span class="dt">group=</span>cut, <span class="dt">fill=</span>cut)) <span class="op">+</span></a>
<a class="sourceLine" id="cb1-12" data-line-number="12"><span class="st"> </span><span class="kw">geom_density</span>(<span class="dt">adjust=</span><span class="fl">1.5</span>) <span class="op">+</span></a>
<a class="sourceLine" id="cb1-13" data-line-number="13"><span class="st"> </span><span class="kw">theme_ipsum</span>()</a>
<a class="sourceLine" id="cb1-14" data-line-number="14"><span class="co">#p1</span></a>
<a class="sourceLine" id="cb1-15" data-line-number="15"></a>
<a class="sourceLine" id="cb1-16" data-line-number="16"><span class="co"># With transparency (right)</span></a>
<a class="sourceLine" id="cb1-17" data-line-number="17">p2 <-<span class="st"> </span><span class="kw">ggplot</span>(<span class="dt">data=</span>diamonds, <span class="kw">aes</span>(<span class="dt">x=</span>price, <span class="dt">group=</span>cut, <span class="dt">fill=</span>cut)) <span class="op">+</span></a>
<a class="sourceLine" id="cb1-18" data-line-number="18"><span class="st"> </span><span class="kw">geom_density</span>(<span class="dt">adjust=</span><span class="fl">1.5</span>, <span class="dt">alpha=</span>.<span class="dv">4</span>) <span class="op">+</span></a>
<a class="sourceLine" id="cb1-19" data-line-number="19"><span class="st"> </span><span class="kw">theme_ipsum</span>()</a>
<a class="sourceLine" id="cb1-20" data-line-number="20"><span class="co">#p2</span></a></code></pre></div>
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<p><img src="135-stacked-density-graph_files/figure-html/unnamed-chunk-2-1.png" width="50%" /><img src="135-stacked-density-graph_files/figure-html/unnamed-chunk-2-2.png" width="50%" /></p>
<p><br><br> Here is an example with <a href="https://www.data-to-viz.com/story/OneNumOneCatSeveralObs.html">another dataset</a> where it works much better. Groups have very distinct distribution, it is easy to spot them even if on the same chart. Note that it is much better to add group name next to their distribution instead of having a legend beside the chart.</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb2-1" data-line-number="1"><span class="co"># Load dataset from github</span></a>
<a class="sourceLine" id="cb2-2" data-line-number="2">data <-<span class="st"> </span><span class="kw">read.table</span>(<span class="st">"https://raw.githubusercontent.com/zonination/perceptions/master/probly.csv"</span>, <span class="dt">header=</span><span class="ot">TRUE</span>, <span class="dt">sep=</span><span class="st">","</span>)</a>
<a class="sourceLine" id="cb2-3" data-line-number="3">data <-<span class="st"> </span>data <span class="op">%>%</span></a>
<a class="sourceLine" id="cb2-4" data-line-number="4"><span class="st"> </span><span class="kw">gather</span>(<span class="dt">key=</span><span class="st">"text"</span>, <span class="dt">value=</span><span class="st">"value"</span>) <span class="op">%>%</span></a>
<a class="sourceLine" id="cb2-5" data-line-number="5"><span class="st"> </span><span class="kw">mutate</span>(<span class="dt">text =</span> <span class="kw">gsub</span>(<span class="st">"</span><span class="ch">\\</span><span class="st">."</span>, <span class="st">" "</span>,text)) <span class="op">%>%</span></a>
<a class="sourceLine" id="cb2-6" data-line-number="6"><span class="st"> </span><span class="kw">mutate</span>(<span class="dt">value =</span> <span class="kw">round</span>(<span class="kw">as.numeric</span>(value),<span class="dv">0</span>))</a>
<a class="sourceLine" id="cb2-7" data-line-number="7"></a>
<a class="sourceLine" id="cb2-8" data-line-number="8"><span class="co"># A dataframe for annotations</span></a>
<a class="sourceLine" id="cb2-9" data-line-number="9">annot <-<span class="st"> </span><span class="kw">data.frame</span>(</a>
<a class="sourceLine" id="cb2-10" data-line-number="10"> <span class="dt">text =</span> <span class="kw">c</span>(<span class="st">"Almost No Chance"</span>, <span class="st">"About Even"</span>, <span class="st">"Probable"</span>, <span class="st">"Almost Certainly"</span>),</a>
<a class="sourceLine" id="cb2-11" data-line-number="11"> <span class="dt">x =</span> <span class="kw">c</span>(<span class="dv">5</span>, <span class="dv">53</span>, <span class="dv">65</span>, <span class="dv">79</span>),</a>
<a class="sourceLine" id="cb2-12" data-line-number="12"> <span class="dt">y =</span> <span class="kw">c</span>(<span class="fl">0.15</span>, <span class="fl">0.4</span>, <span class="fl">0.06</span>, <span class="fl">0.1</span>)</a>
<a class="sourceLine" id="cb2-13" data-line-number="13">)</a>
<a class="sourceLine" id="cb2-14" data-line-number="14"></a>
<a class="sourceLine" id="cb2-15" data-line-number="15"><span class="co"># Plot</span></a>
<a class="sourceLine" id="cb2-16" data-line-number="16">data <span class="op">%>%</span></a>
<a class="sourceLine" id="cb2-17" data-line-number="17"><span class="st"> </span><span class="kw">filter</span>(text <span class="op">%in%</span><span class="st"> </span><span class="kw">c</span>(<span class="st">"Almost No Chance"</span>, <span class="st">"About Even"</span>, <span class="st">"Probable"</span>, <span class="st">"Almost Certainly"</span>)) <span class="op">%>%</span></a>
<a class="sourceLine" id="cb2-18" data-line-number="18"><span class="st"> </span><span class="kw">ggplot</span>( <span class="kw">aes</span>(<span class="dt">x=</span>value, <span class="dt">color=</span>text, <span class="dt">fill=</span>text)) <span class="op">+</span></a>
<a class="sourceLine" id="cb2-19" data-line-number="19"><span class="st"> </span><span class="kw">geom_density</span>(<span class="dt">alpha=</span><span class="fl">0.6</span>) <span class="op">+</span></a>
<a class="sourceLine" id="cb2-20" data-line-number="20"><span class="st"> </span><span class="kw">scale_fill_viridis</span>(<span class="dt">discrete=</span><span class="ot">TRUE</span>) <span class="op">+</span></a>
<a class="sourceLine" id="cb2-21" data-line-number="21"><span class="st"> </span><span class="kw">scale_color_viridis</span>(<span class="dt">discrete=</span><span class="ot">TRUE</span>) <span class="op">+</span></a>
<a class="sourceLine" id="cb2-22" data-line-number="22"><span class="st"> </span><span class="kw">geom_text</span>( <span class="dt">data=</span>annot, <span class="kw">aes</span>(<span class="dt">x=</span>x, <span class="dt">y=</span>y, <span class="dt">label=</span>text, <span class="dt">color=</span>text), <span class="dt">hjust=</span><span class="dv">0</span>, <span class="dt">size=</span><span class="fl">4.5</span>) <span class="op">+</span></a>
<a class="sourceLine" id="cb2-23" data-line-number="23"><span class="st"> </span><span class="kw">theme_ipsum</span>() <span class="op">+</span></a>
<a class="sourceLine" id="cb2-24" data-line-number="24"><span class="st"> </span><span class="kw">theme</span>(</a>
<a class="sourceLine" id="cb2-25" data-line-number="25"> <span class="dt">legend.position=</span><span class="st">"none"</span></a>
<a class="sourceLine" id="cb2-26" data-line-number="26"> ) <span class="op">+</span></a>
<a class="sourceLine" id="cb2-27" data-line-number="27"><span class="st"> </span><span class="kw">ylab</span>(<span class="st">""</span>) <span class="op">+</span></a>
<a class="sourceLine" id="cb2-28" data-line-number="28"><span class="st"> </span><span class="kw">xlab</span>(<span class="st">"Assigned Probability (%)"</span>)</a></code></pre></div>
<p><img src="135-stacked-density-graph_files/figure-html/unnamed-chunk-3-1.png" width="80%" style="display: block; margin: auto;" /></p>
<h1 id="smallMulti">Small Multiple with <code>facet_wrap()</code></h1>
<hr />
<p>Using small multiple is often the best option in my opinion. Distribution of each group gets easy to read, and comparing groups is still possible if they share the same X axis boundaries.</p>
<div class="sourceCode" id="cb3"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb3-1" data-line-number="1"><span class="co"># Using Small multiple</span></a>
<a class="sourceLine" id="cb3-2" data-line-number="2"><span class="kw">ggplot</span>(<span class="dt">data=</span>diamonds, <span class="kw">aes</span>(<span class="dt">x=</span>price, <span class="dt">group=</span>cut, <span class="dt">fill=</span>cut)) <span class="op">+</span></a>
<a class="sourceLine" id="cb3-3" data-line-number="3"><span class="st"> </span><span class="kw">geom_density</span>(<span class="dt">adjust=</span><span class="fl">1.5</span>) <span class="op">+</span></a>
<a class="sourceLine" id="cb3-4" data-line-number="4"><span class="st"> </span><span class="kw">theme_ipsum</span>() <span class="op">+</span></a>
<a class="sourceLine" id="cb3-5" data-line-number="5"><span class="st"> </span><span class="kw">facet_wrap</span>(<span class="op">~</span>cut) <span class="op">+</span></a>
<a class="sourceLine" id="cb3-6" data-line-number="6"><span class="st"> </span><span class="kw">theme</span>(</a>
<a class="sourceLine" id="cb3-7" data-line-number="7"> <span class="dt">legend.position=</span><span class="st">"none"</span>,</a>
<a class="sourceLine" id="cb3-8" data-line-number="8"> <span class="dt">panel.spacing =</span> <span class="kw">unit</span>(<span class="fl">0.1</span>, <span class="st">"lines"</span>),</a>
<a class="sourceLine" id="cb3-9" data-line-number="9"> <span class="dt">axis.ticks.x=</span><span class="kw">element_blank</span>()</a>
<a class="sourceLine" id="cb3-10" data-line-number="10"> )</a></code></pre></div>
<p><img src="135-stacked-density-graph_files/figure-html/unnamed-chunk-4-1.png" width="80%" style="display: block; margin: auto;" /></p>
<h1 id="stacked">Stacked density chart</h1>
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<p>Another solution is to <u>stack</u> the groups. This allows to see what group is the most frequent for a given value, but it makes it hard to understand the distribution of a group that is not on the bottom of the chart.</p>
<p>Visit <a href="https://www.data-to-viz.com/caveat/stacking.html">data to viz</a> for a complete explanation on this matter.</p>
<div class="sourceCode" id="cb4"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb4-1" data-line-number="1"><span class="co"># Stacked density plot:</span></a>
<a class="sourceLine" id="cb4-2" data-line-number="2">p <-<span class="st"> </span><span class="kw">ggplot</span>(<span class="dt">data=</span>diamonds, <span class="kw">aes</span>(<span class="dt">x=</span>price, <span class="dt">group=</span>cut, <span class="dt">fill=</span>cut)) <span class="op">+</span></a>
<a class="sourceLine" id="cb4-3" data-line-number="3"><span class="st"> </span><span class="kw">geom_density</span>(<span class="dt">adjust=</span><span class="fl">1.5</span>, <span class="dt">position=</span><span class="st">"fill"</span>) <span class="op">+</span></a>
<a class="sourceLine" id="cb4-4" data-line-number="4"><span class="st"> </span><span class="kw">theme_ipsum</span>()</a>
<a class="sourceLine" id="cb4-5" data-line-number="5"><span class="co">#p</span></a></code></pre></div>
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</footer>
<script>
// add bootstrap table styles to pandoc tables
function bootstrapStylePandocTables() {
$('tr.header').parent('thead').parent('table').addClass('table table-condensed');
}
$(document).ready(function () {
bootstrapStylePandocTables();
});
</script>
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<!-- Bootstrap core JavaScript -->
<script src="vendor/bootstrap/js/bootstrap.bundle.min.js"></script>
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<script src="js/agency.min.js"></script>
</body>
</html>