Forzaa Forzaa - 1 year ago 93
R Question

R: bar plot with two groups, of which one is stacked

I've encountered a small problem when creating a bar plot in R. There are 3 variables:

a <- c(3,3,2,1,0)
b <- c(3,2,2,2,2)
c <- 0:4

The bar plot should be grouped by 'a' and 'c', and 'b' should be stacked on top of 'a'. Doing the grouping and stacking seperately is straightforward:

barplot(rbind(a,c), beside=TRUE)
barplot(rbind(a,b), beside=FALSE)

How can you do both at once in one graph?

Answer Source

Doing this requires thinking about how barplot draws stacked bars. Basically, you need to feed it some data with 0 values in appropriate places. With your data:

mydat <- cbind(rbind(a,b,0),rbind(0,0,c))[,c(1,6,2,7,3,8,4,9,5,10)]


To see what's going on under the hood, take a look at mydat:

> mydat
  [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
a    3    0    3    0    2    0    1    0    0     0
b    3    0    2    0    2    0    2    0    2     0
     0    0    0    1    0    2    0    3    0     4

Here, you're plotting each bar with three values (the value of a, the value of b, the value of c). Each column of the mydat matrix is a bar, sorted so that the ab bars are appropriately interspersed with the c bars. You may want to play around with spacing and color.

Apparently versions of this have been discussed on R-help various times without great solutions, so hopefully this is helpful.

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