title: stat_compare_means anova on selected groups
body: <p>I would like to compute an anova only including gr1-gr3 excluding gr4. Is this possible using <code>stat_compare_means()</code>?</p>
  
  <pre><code>x   value
  gr1 3.543
  gr1 2.12
  gr1 4.56
  gr2 3.3
  gr2 2.12
  gr2 4.1
  gr3 3.32
  gr3 2.3
  gr3 3.3
  gr4 3.325
  gr4 2.355
  gr4 3.34
  
  library(ggpubr)
  ggplot(df(aes(x,value)) + geom_boxplot() + stat_compare_means()
  </code></pre>