R：更改堆叠条形图中各个条的颜色

Question

Using base graphics, I got a barchart like this one

a <- c(1,2,3); b <- c(1,1,1)
barplot(rbind(a,b), col=c("red","gray"))

with each bar grey at the top and red at the bottom. However, I would like each bar to change the color at the bottom and keep the grey at the top.

cols <- c(rbind(c("red","green","blue"),"gray"))
barplot(rbind(a,b), col=cols) 

did not do the trick. Is there any other way?

Answer 1

Not the most elegant way but this works.

a<-c(1,1,1)
b<-c(1,0,0)
c<-c(0,2,0)
d<-c(0,0,3)

cols <-c("red","green","blue","gray")
# notice order of rbind... a is last
barplot(rbind(b,c,d,a), col=cols )