title: Indicating significance with ggplot2, in a boxplot with multiple groups
body: <p>I have the following plot made with ggplot2 and ggpubr. I would like to indicate significance between VaD+ and HC. I would like to change the p-values to asterisks. I think I'm supposed to use symnum.args, but when I try it, I get no change.</p>
  
  <pre><code>myplot &lt;- ggplot(my.data, aes(x = DX, y = CC, fill=DX)) + geom_boxplot() + ggtitle("Corpus Collasum") + theme(text=element_text(size = 16), panel.grid.major = element_blank(), panel.grid.minor = element_blank(),panel.background = element_blank(), axis.line = element_line(colour = "black"), plot.title = element_text(lineheight=.8, face="bold", hjust=0.5)) + scale_y_continuous(name = bquote('Volume in'~mm^3)) + scale_x_discrete(name = "Diagnosis", labels = c("AD","HC","VaD-","VaD+")) + scale_fill_brewer(palette="OrRd", name="Diagnosis", labels=c("AD","HC","VaD-","VaD+")) + geom_jitter(width = 0)
  cmpr &lt;- list(c("VaDD","HC"), c("AD","VaDD"))
  myplot + stat_compare_means(comparisons = cmpr, tip.length=0.01, symnum &lt;- list(cutpoints = c(0, 0.0001, 0.001, 0.01, 0.05, 1), symbols = c("****", "***", "**", "*", "ns")))
  </code></pre>
  
  <p>Basically I would like to replace the numeric p-values by the symbol.</p>
  
  <p><a href="https://gitlab.com/elijahrockers/tmp/raw/master/vascular-subcort.csv" rel="nofollow noreferrer">Here</a> is the data.</p>
  
  <p><img src="https://i.stack.imgur.com/euwcH.png" alt="this plot"></p>