Forzaa - 4 months ago 28

R Question

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

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)]
barplot(mydat,space=c(.75,.25))
```

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.