Adding a key legend to a graph with multiple histograms in R

Question

How to add a key legend to the figure below

I want to have a key legend somewhere in the upper right corner with two short horizontal stripes of color, where red should say: “Plastic surgery went wrong,” and blue “Germany.”

I used the following code to create a graph:

bar2 <- read.table("div/ana-mut[...]/barriers-set-2.dat", sep=" ") bar2val <- c(bar2$V1, bar2$V2) bar3 <- read.table("div/ana-mut[...]/barriers-set-3.dat", sep=" ") bar3val <- c(bar3$V1, bar3$V2) p1 <- hist(subset(bar2val, bar2val < 30), breaks=30) p2 <- hist(subset(bar3val, bar3val < 30), breaks=30) plot(p1, col=rgb(1,0,0,8/9), main="Barrier distribution", xlab="Barrier [kcal/mol]", ylab="Mutant count") plot(p2, col=rgb(0,0,1,8/9), add=T) 

Any hints would be greatly appreciated.

Answer 1

The legend command will do the trick:

 legend("topright", c("Germany", "Plastic"), col=c("blue", "red"), lwd=10) 

To get two short horizontal stripes of color, use the standard line, but increase the thickness of the line. As Roland pointed out, you can also use the fill argument:

 legend("topright", c("Germany", "Plastic"), fill=c("blue", "red")) 

See ?legend more details.

Answer 2

here is an alternative solution (see below code)

 # some semi-random data … df <- structure(list(Germany = c(1L, 3L, 6L, 1L, 2L), Plastic = c(2L, 5L, 4L, 2L, 3L)), .Names = c("Germany", "Plastic"), class = "data.frame", row.names = c(NA, -5L)) # Expand right side of clipping rect to make room for the legend par(xpd=T, mar=par()$mar+c(0,0,0,4)) # Graph data (transposing the matrix) using heat colors, # put 10% of the space between each bar, and make labels # smaller with horizontal y-axis labels barplot(t(df), main="Barrier distribution", xlab="Barrier [kcal/mol]", ylab="Mutant count", col=c("blue", "red"), space=0.1, cex.axis=0.8, las=1, names.arg=c("Mon","Tue","Wed","Thu","Fri"), cex=0.8) # Place the legend at (4,9) using blue and red legend(4, 9, names(df), lwd=4, col=c("blue", "red")) # Restore default clipping rect par(mar=c(5, 4, 4, 2) + 0.1)