I’ve been a big fan of ggplot2 for a long time but plyr has been in my toolkit for less than a year and it is now one of my most-used R packages. It is how aggregate/*apply would have been if they were awesome.
In five lines this code computes the cumulative distribution functions of all of the variables in the iris data set and creates a colored, faceted plot to visualize the data.
#cummulative distribution of iris data
# 0.1% increments
#compute quantiles by species for each variable
#melt the data.frame for easy ggplot faceting on variable
# plot using color for species and facets for variables
p+geom_point(aes(color = factor(Species)))+facet_wrap(~variable)