Learn how to group data for ggplot

grouping.R

library(ggplot2)
unique(diamonds$cut)
unique(diamonds$color)
names(diamonds)
h <- ggplot(diamonds[1:1000,], aes(x=cut)) + geom_bar(); h #simple histogram
h <- ggplot(diamonds[1:1000,], aes(x=cut, fill=color)) + geom_bar(); h # stacked by default
h <- ggplot(diamonds[1:1000,], aes(x=cut, fill=color)) + geom_bar(position="dodge"); h #unstack using dodge
h

grouping_with_ddply.R

#add a new column to the data.frame
iris2 <- ddply(iris, "Species", transform,  avg.petal = mean(Petal.Length))
ggplot(iris2) + geom_boxplot(aes(x=Species, y=avg.petal))
ggplot(iris2) + geom_bar(aes(x=Species, y=avg.petal))