plot - R graphics: add labels to clustered/dodged bar chart -

this basic plotting question:

i need add labels clustered/dodged bar chart. have looked @ several examples using text(), cannot seem position labels correctly.

teachers <- c("a", "b","c", "d", "e") mean_pre_scores <- c(10, 11, 12, 10,9) mean_post_scores <- c(12,15,17,13,12) pre_post <- data.frame(mean_pre_scores, mean_post_scores)  pre_post <- as.matrix(pre_post) barplot((t(pre_post)), beside = t, names = teachers, legend = c("pre", "post"),          ylim = c(0,20), args.legend = list(x="bottomright"),  axes = t, main = "unit 1 test",         col=c(26,51)) 

i want modify plot values displayed above bars. helpful know how show values inside bars.

i think you're after:

z <- barplot((t(pre_post)), beside = t, names = teachers,      legend = c("pre", "post"), ylim = c(0,20),      args.legend = list(x="topright"),  axes = t,      main = "unit 1 content pre test", col=c(26,51))  text(cex=1, x=c(z[1, ], z[2, ]), y=c(pre_post) + par("cxy")[2]/2, c(pre_post), xpd=true)  

to move text inside bars use subtractions in:

text(cex=1, x=c(z[1, ], z[2, ]), y=c(pre_post) - par("cxy")[2]/2, c(pre_post), xpd=true)