title: Align violin plots with dodged box plots
body: <p>I have this data frame</p>
  <pre><code>set.seed(1234)
  x &lt;- rnorm(80, 5, 1)
  df &lt;- data.frame(groups = c(rep(&quot;group1&quot;,20),
                             rep(&quot;group2&quot;,20),
                             rep(&quot;group3&quot;,20),
                             rep(&quot;group4&quot;,20)),
                      value = x,
                      type = c(rep(&quot;A&quot;, 10),
                             rep(&quot;B&quot;, 10),
                             rep(&quot;A&quot;, 10),
                             rep(&quot;B&quot;, 10),
                             rep(&quot;A&quot;, 10),
                             rep(&quot;B&quot;, 10),
                             rep(&quot;A&quot;, 10),
                             rep(&quot;B&quot;, 10)))
  </code></pre>
  <p>And I would like to plot it as violin plot, aligned with a narrow box plot and grouped by 'type':</p>
  <pre><code>ggplot(data = df, aes(x = groups, y = value, fill = type)) +
    geom_violin()+
    geom_boxplot(width = 0.1, outlier.colour = NA)
  </code></pre>
  <p>However, the box plots does not align to the violin plots. What is the missing argument to tell ggplot to do such overlying?</p>
  <p>Thanks!</p>