HairEyeColor data set. This type of plot is called a grouped bar plot.
Grouped bar plot of Eye Color and Hair Color in 313 female students.How does the base R graphics package deal with that? You begin by isolating the female data in the HairEyeColor data set, which lives in the datasets package:
> library(datasets)
> females <- HairEyeColor[,,2] > females
Eye
Hair Brown Blue Hazel Green
Black 36 9 5 2
Brown 66 34 29 14
Red 16 7 7 7
Blond 4 64 5 8
To begin producing the image above, you have to specify the colors in the bars and in the legend:> color.names = c("black","grey40","grey80","white")
A word about those names: You can combine grey with any number from 0 to 100 to create a color — “grey0” is equivalent to “black” and “grey100” is equivalent to “white”.
Now you turn once again to the barplot() function. Interestingly, if you use females as the first argument for barplot(), R draws a plot with Eye Color on the x-axis (rather than Hair Color). To reverse that, you use t() to interchange (transpose, in other words) the rows and columns:
> t(females)
Hair
Eye Black Brown Red Blond
Brown 36 66 16 4
Blue 9 34 7 64
Hazel 5 29 7 5
Green 2 14 7 8
The function that produces the bar plot is
> barplot(t(females),beside=T,ylim=c(0,70),xlab="Hair Color",ylab="Frequency of Eye
Color", col=color.names,axis.lty="solid")
beside=T tells R to plot the bars, well, beside each other. (Try it without this argument and watch what happens.) ylim insures that no bar will rise above the highest value on the y-axis. col=color.names supplies the colors named in the vector.The plot isn’t complete without the legend (the box that tells you which plot colors correspond to which eye colors):
> legend("top",rownames(t(females)),cex =0.8,fill=color.names,title="Eye Color")
The first argument puts the legend at the top of the plot, and the second argument provides the names. The third argument specifies the size of the characters in the legend — .08 means “80% of the normal size.” The fourth argument gives the colors for the color swatches, and the fifth, of course, provides the title.