arranging order of stacked geom_bar in ggplot2

Question

I am drawing some pie charts using facet_wrap and coord_polar, let say I have factors with sequence A,B,C.D, for the x-axis, and by using the facet_wrap (for 3 charts, let say) and coord_polar. I will have 3 pies (pie X,Y,Z) with arranged as A,B,C.D in clockwise direction.

Problem arise when I want to re-arrange the level of the factor individually for each facet, e.g.:

   A  B  C  D
X 10 20 30 40
Y 20 30 40 10
Z 30 40 10 20

I want:

pie X to be arranged as : A,B,C.D clockwise

pie Y to be arranged as : D,A,B.C clockwise

pie Z to be arranged as : C,D,A.B clockwise

Can I do that in ggplot2? Thanks.

Answer 1

The grid/viewport approach would work something like this. First we arrange some data to match what you show. We rotate the levels of the factor for each of X, Y and Z as you specify in the question

## Your data
dat <- data.frame(X = factor(rep(LETTERS[1:4], times = c(10,20,30,40)), 
                             levels = LETTERS[1:4]),
                  Y = factor(rep(LETTERS[1:4], times = c(20,30,40,10)),
                             levels = LETTERS[c(4,1:3)]),
                  Z = factor(rep(LETTERS[1:4], times = c(30,40,10,20)),
                             levels = LETTERS[c(3:4,1:2)]))

Next we produce the individual pie plots, rotating the same scale_fill_manual() colours in the same order we rotated the levels in the data, dat (with apologies for the nasty colours - how does one get the first n colours that ggplot would use normally?):

p1 <- ggplot(dat, aes(x = factor(1), fill = factor(X))) + 
          geom_bar(width = 1) + coord_polar(theta = "y") +
          scale_fill_manual(value = c("red","green","yellow","blue"))
p2 <- ggplot(dat, aes(x = factor(1), fill = factor(Y))) + 
          geom_bar(width = 1) + coord_polar(theta = "y") +
          scale_fill_manual(value = c("red","green","yellow","blue")[c(4,1:3)])
p3 <- ggplot(dat, aes(x = factor(1), fill = factor(Z))) + 
          geom_bar(width = 1) + coord_polar(theta = "y") +
          scale_fill_manual(value = c("red","green","yellow","blue")[c(3:4,1:2)])

Now we need a new plotting page and to push onto it a 2x2 layout:

grid.newpage()
pushViewport(viewport(layout = grid.layout(2,2)))

A custom function allows us to simplify setting the row/col for each subsequent plot:

vplayout <- function(x, y) {
    viewport(layout.pos.row = x, layout.pos.col = y)
}

Next we simply plot each save ggplot object on the correct viewport, as specified by argument vp:

print(p1, vp = vplayout(1,1))
print(p2, vp = vplayout(1,2))
print(p3, vp = vplayout(2,1))

The above grid code was taken from page 94 in Hadley's excellent book on ggplot.

This produces: