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<center><h1>Most basic violin plot with ggplot2</h1></center>
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<center><p style="max-width: 600px; margin-top: 40px">A <a href="violin.html">violin plot</a> allows to compare the distribution of several groups by displaying their densities. See how to build it with <code>R</code> and <code>ggplot2</code> below. Learn more about violin chart theory in <a href="https://www.data-to-viz.com/graph/violin.html">data-to-viz</a>.</p></center>
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<a class="btn btn-secondary btn-xl text-uppercase js-scroll-trigger" href='violin.html'>Violin Section</a>
<a class="btn btn-secondary btn-xl text-uppercase js-scroll-trigger" href='https://www.data-to-viz.com/graph/violin.html'>Violin theory</a>
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<h1 id="basic-violin-plot">Basic violin plot</h1>
<hr />
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<div class="col-md-6 col-sm-12 align-self-center">
<p>Building a <a href="violin.html">violin plot</a> with <code>ggplot2</code> is pretty straightforward thanks to the dedicated <code>geom_violin()</code> function.</p>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r"><span class="co"># Library</span>
<span class="kw">library</span>(ggplot2)
<span class="co"># create a dataset</span>
data <-<span class="st"> </span><span class="kw">data.frame</span>(
<span class="dt">name=</span><span class="kw">c</span>( <span class="kw">rep</span>(<span class="st">"A"</span>,<span class="dv">500</span>), <span class="kw">rep</span>(<span class="st">"B"</span>,<span class="dv">500</span>), <span class="kw">rep</span>(<span class="st">"B"</span>,<span class="dv">500</span>), <span class="kw">rep</span>(<span class="st">"C"</span>,<span class="dv">20</span>), <span class="kw">rep</span>(<span class="st">'D'</span>, <span class="dv">100</span>) ),
<span class="dt">value=</span><span class="kw">c</span>( <span class="kw">rnorm</span>(<span class="dv">500</span>, <span class="dv">10</span>, <span class="dv">5</span>), <span class="kw">rnorm</span>(<span class="dv">500</span>, <span class="dv">13</span>, <span class="dv">1</span>), <span class="kw">rnorm</span>(<span class="dv">500</span>, <span class="dv">18</span>, <span class="dv">1</span>), <span class="kw">rnorm</span>(<span class="dv">20</span>, <span class="dv">25</span>, <span class="dv">4</span>), <span class="kw">rnorm</span>(<span class="dv">100</span>, <span class="dv">12</span>, <span class="dv">1</span>) )
)
<span class="co"># Most basic violin chart</span>
p <-<span class="st"> </span><span class="kw">ggplot</span>(data, <span class="kw">aes</span>(<span class="dt">x=</span>name, <span class="dt">y=</span>value, <span class="dt">fill=</span>name)) <span class="op">+</span><span class="st"> </span><span class="co"># fill=name allow to automatically dedicate a color for each group</span>
<span class="st"> </span><span class="kw">geom_violin</span>()
<span class="co">#p</span></code></pre></div>
</div>
<div class="col-md-6 col-sm-12">
<p><img src="95-violin-plot-with-ggplot2_files/figure-html/unnamed-chunk-2-1.png" width="100%" /></p>
</div>
</div>
<h1 id="note-on-input-format">Note on input format</h1>
<hr />
<p>Ggplot2 expects input data to be in a <em>long</em> format: each row is dedicated to <em>one</em> observation. Your input needs 2 column:<br />
- a <em>categorical</em> variable for the X axis: it needs to be have the class <code>factor</code><br />
- a <em>numeric</em> variable for the Y axis: it needs to have the class <code>numeric</code> <br></p>
<div class="row">
<div class="col-md-6 col-sm-12">
<h3 id="from-long-format">→ From long format</h3>
<p>You already have the good format. It’s going to be a breeze to plot it with <code>geom_violin()</code> as follow:</p>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r"><span class="co"># Library</span>
<span class="kw">library</span>(ggplot2)
<span class="kw">library</span>(dplyr)
<span class="co"># Create data</span>
data <-<span class="st"> </span><span class="kw">data.frame</span>(
<span class="dt">name=</span><span class="kw">c</span>( <span class="kw">rep</span>(<span class="st">"A"</span>,<span class="dv">500</span>), <span class="kw">rep</span>(<span class="st">"B"</span>,<span class="dv">500</span>), <span class="kw">rep</span>(<span class="st">"B"</span>,<span class="dv">500</span>), <span class="kw">rep</span>(<span class="st">"C"</span>,<span class="dv">20</span>), <span class="kw">rep</span>(<span class="st">'D'</span>, <span class="dv">100</span>) ),
<span class="dt">value=</span><span class="kw">c</span>( <span class="kw">rnorm</span>(<span class="dv">500</span>, <span class="dv">10</span>, <span class="dv">5</span>), <span class="kw">rnorm</span>(<span class="dv">500</span>, <span class="dv">13</span>, <span class="dv">1</span>), <span class="kw">rnorm</span>(<span class="dv">500</span>, <span class="dv">18</span>, <span class="dv">1</span>), <span class="kw">rnorm</span>(<span class="dv">20</span>, <span class="dv">25</span>, <span class="dv">4</span>), <span class="kw">rnorm</span>(<span class="dv">100</span>, <span class="dv">12</span>, <span class="dv">1</span>) ) <span class="op">%>%</span><span class="st"> </span><span class="kw">round</span>(<span class="dv">2</span>)
)</code></pre></div>
<table class="table table-striped table-hover table-condensed" style="width: auto !important; margin-left: auto; margin-right: auto;">
<thead>
<tr>
<th style="text-align:center;">
name
</th>
<th style="text-align:center;">
value
</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align:center;">
A
</td>
<td style="text-align:center;">
18.64
</td>
</tr>
<tr>
<td style="text-align:center;">
A
</td>
<td style="text-align:center;">
3.18
</td>
</tr>
<tr>
<td style="text-align:center;">
A
</td>
<td style="text-align:center;">
10.81
</td>
</tr>
<tr>
<td style="text-align:center;">
A
</td>
<td style="text-align:center;">
14.00
</td>
</tr>
</tbody>
</table>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r"><span class="co"># Basic violin</span>
<span class="kw">ggplot</span>(data, <span class="kw">aes</span>(<span class="dt">x=</span>name, <span class="dt">y=</span>value, <span class="dt">fill=</span>name)) <span class="op">+</span><span class="st"> </span>
<span class="st"> </span><span class="kw">geom_violin</span>()</code></pre></div>
<p><img src="95-violin-plot-with-ggplot2_files/figure-html/unnamed-chunk-5-1.png" width="100%" /></p>
</div>
<div class="col-md-6 col-sm-12">
<h3 id="from-wide-format">→ From wide format</h3>
<p>In this case we need to reformat the input. This is possible thanks to the <code>gather()</code> function of the <code>tidyr</code> library that is part of the <code>tidyverse</code>.</p>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r"><span class="co"># Let's use the iris dataset as an example:</span>
data_wide <-<span class="st"> </span>iris[ , <span class="dv">1</span><span class="op">:</span><span class="dv">4</span>]</code></pre></div>
<table class="table table-striped table-hover table-condensed" style="width: auto !important; margin-left: auto; margin-right: auto;">
<thead>
<tr>
<th style="text-align:center;">
Sepal.Length
</th>
<th style="text-align:center;">
Sepal.Width
</th>
<th style="text-align:center;">
Petal.Length
</th>
<th style="text-align:center;">
Petal.Width
</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align:center;">
5.1
</td>
<td style="text-align:center;">
3.5
</td>
<td style="text-align:center;">
1.4
</td>
<td style="text-align:center;">
0.2
</td>
</tr>
<tr>
<td style="text-align:center;">
4.9
</td>
<td style="text-align:center;">
3.0
</td>
<td style="text-align:center;">
1.4
</td>
<td style="text-align:center;">
0.2
</td>
</tr>
<tr>
<td style="text-align:center;">
4.7
</td>
<td style="text-align:center;">
3.2
</td>
<td style="text-align:center;">
1.3
</td>
<td style="text-align:center;">
0.2
</td>
</tr>
<tr>
<td style="text-align:center;">
4.6
</td>
<td style="text-align:center;">
3.1
</td>
<td style="text-align:center;">
1.5
</td>
<td style="text-align:center;">
0.2
</td>
</tr>
</tbody>
</table>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r"><span class="kw">library</span>(tidyr)
data_wide <span class="op">%>%</span><span class="st"> </span>
<span class="st"> </span><span class="kw">gather</span>(<span class="dt">key=</span><span class="st">"MesureType"</span>, <span class="dt">value=</span><span class="st">"Val"</span>) <span class="op">%>%</span>
<span class="st"> </span><span class="kw">ggplot</span>( <span class="kw">aes</span>(<span class="dt">x=</span>MesureType, <span class="dt">y=</span>Val, <span class="dt">fill=</span>MesureType)) <span class="op">+</span>
<span class="st"> </span><span class="kw">geom_violin</span>()</code></pre></div>
<p><img src="95-violin-plot-with-ggplot2_files/figure-html/unnamed-chunk-8-1.png" width="100%" /></p>
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