Drawing multiple barplots on a graph in R

Question

I would like to plot four barplots on a single graph in R. I have used the following code. Here, how can keep a legend on top of the graph, specifically the legend should be between 2 and 3 barplots. I also tried with par(mar=c(4.1,4.1,8.1,4.1) but there is no success. Moreover, I also tried to run legend() after the second barplot, but there is no use. The legend is for all the four barplots. Please help me in this.

    par(mfrow=c(1,4))
    barplot(t(A), beside=T, ylim=c(-100,100),..)
    barplot(t(B), beside=T, ylim=c(-100,100),..)
    barplot(t(C), beside=T, ylim=c(-100,100),..)
    barplot(t(D), beside=T, ylim=c(-100,100),..)
    legend(...)

Answer 1

Dr. Mike's answer is a good one, but I thought I'd provide solutions that take advantage of the faceting (or trellising) features of ggplot2 and lattice. First prep the data slightly:

mydata$id <- 1:nrow(mydata)
dat <- melt(mydata,id.vars = "id")

and then we can make the following in ggplot2:

ggplot(dat,aes(x=factor(id), y = value)) + 
    facet_wrap(~variable) +
    geom_bar(aes(fill = factor(id)))

and using lattice:

barchart(~value|variable,group = factor(id),data=dat,
         key = simpleKey(text = as.character(1:5),
                rectangles = TRUE,points = FALSE,space = "right"))

Answer 2

I think the most simple solution is to use barplot command's inherent capabilities to solve your problem. The following code does what I interpret that you want done.

mydata <- data.frame(Barplot1=rbinom(5,16,0.6), Barplot2=rbinom(5,16,0.25),
                     Barplot3=rbinom(5,5,0.25), Barplot4=rbinom(5,16,0.7))
barplot(as.matrix(mydata), main="Interesting", ylab="Total", beside=TRUE, 
        col=terrain.colors(5))
legend(13, 12, c("Label1","Label2","Label3","Label4","Label5"), cex=0.6, 
       fill=terrain.colors(5))

Hope this answers your question.