GNU R significance brackets for ggplot2

 Enrich your 'ggplots' with group-wise comparisons. This package provides
 an easy way to indicate if two groups are significantly different.
 Commonly this is shown by a bracket on top connecting the groups of
 interest which itself is annotated with the level of significance (NS,
  *, **, ***). The package provides a single layer (geom_signif()) that
 takes the groups for comparison and the test (t.test(), wilcox.text()
 etc.) as arguments and adds the annotation to the plot.