title: Split Violin Plot with 3 groups
body: <p>Just find how to create a split violin plot from <a href="https://stackoverflow.com/questions/35717353/split-violin-plot-with-ggplot2" title="here">here</a> and then how to extend this for more than two groups from <a href="https://stackoverflow.com/questions/43502947/r-ggplot2-split-violin-plot-with-more-than-2-groups">here</a>. But I do not understand how to tranfer this to my own data.</p>
  
  <p>Now, I am stuck in creating my own split violin plot.</p>
  
  <p>I am aiming for something like <a href="https://i.stack.imgur.com/4EZrQ.jpg" rel="nofollow noreferrer">this</a>; each group should represent one cancer entity (left the reference incidence, right the cohort's incidence). </p>
  
  <p>Following the first link (see above), I used this code to create the function geom_split_violin</p>
  
  <pre><code>GeomSplitViolin &lt;- ggproto("GeomSplitViolin", GeomViolin, draw_group = function(self, data, ..., draw_quantiles = NULL){
    data &lt;- transform(data, xminv = x - violinwidth * (x - xmin), xmaxv = x + violinwidth * (xmax - x))
    grp &lt;- data[1,'group']
    newdata &lt;- plyr::arrange(transform(data, x = if(grp%%2==1) xminv else xmaxv), if(grp%%2==1) y else -y)
    newdata &lt;- rbind(newdata[1, ], newdata, newdata[nrow(newdata), ], newdata[1, ])
    newdata[c(1,nrow(newdata)-1,nrow(newdata)), 'x'] &lt;- round(newdata[1, 'x']) 
    if (length(draw_quantiles) &gt; 0 &amp; !scales::zero_range(range(data$y))) {
      stopifnot(all(draw_quantiles &gt;= 0), all(draw_quantiles &lt;= 
                                                1))
      quantiles &lt;- create_quantile_segment_frame(data, draw_quantiles)
      aesthetics &lt;- data[rep(1, nrow(quantiles)), setdiff(names(data), c("x", "y")), drop = FALSE]
      aesthetics$alpha &lt;- rep(1, nrow(quantiles))
      both &lt;- cbind(quantiles, aesthetics)
      quantile_grob &lt;- GeomPath$draw_panel(both, ...)
      ggplot2:::ggname("geom_split_violin", grobTree(GeomPolygon$draw_panel(newdata, ...), quantile_grob))
    }
    else {
      ggplot2:::ggname("geom_split_violin", GeomPolygon$draw_panel(newdata, ...))
    }
  })
  
  geom_split_violin &lt;- function (mapping = NULL, data = NULL, stat = "ydensity", position = "identity", ..., draw_quantiles = NULL, trim = TRUE, scale = "area", na.rm = FALSE, show.legend = NA, inherit.aes = TRUE) {
    layer(data = data, mapping = mapping, stat = stat, geom = GeomSplitViolin, position = position, show.legend = show.legend, inherit.aes = inherit.aes, params = list(trim = trim, scale = scale, draw_quantiles = draw_quantiles, na.rm = na.rm, ...))
  }
  </code></pre>
  
  <p>I do not understand the full code above and guess, that this code will create a split violin plot with only two groups.</p>
  
  <p>Hopefully, my request is not to general and you guys can show my a way how to reach my plot.</p>
  
  <p>All I reached is</p>
  
  <pre><code>my_data &lt;- read.csv("Test2.csv", sep = ";")
  
  y &lt;- data_vp$Age.groups
  x &lt;- cbind(data_vp[,3:8])
  m &lt;- cbind(data_vp[,3:5], data_vp[,6:8])
  
  ggplot(my_data,
         aes(x = x,
             y = y,
             fill = m)) + 
    geom_split_violin()
  </code></pre>
  
  <p>After getting your answer @missuse I tried again with this code:</p>
  
  <pre><code>raw_df &lt;- read.csv("Test2.csv", sep = ";")
  View(raw_df)
  
  inc_all &lt;- raw_df[,2:7]
  inc_oM &lt;- raw_df[,2:4]
  inc_mM &lt;- raw_df[,5:7]
  
  
  dff &lt;- data.frame(y = raw_df$Age.groups,
                    groups = as.factor(inc_all),
                    split = as.factor(inc_oM + inc_mM))
  
  ggplot(dff, 
         aes(x = groups,
             y = y,
             fill = split)) + 
    geom_split_violin()
  </code></pre>
  
  <p>Does not work :( </p>