ggplot2: Add label on barplot if position = “fill”

Question

I would like to add %-figures on a filled barplot. Here is the plot with the labels at the wrong places:

Here is the dataframe:

x0 <- expand.grid(grp    = c("G1","G2")
                 , treat = c("T1","T2")
                 , out   = c("out1","out2","out3","out4")
)
set.seed(1234)
x0$n <- round(runif(16,0,1)*100,0)
head(x0)
  grp treat  out  n
1  G1    T1 out1 11
2  G2    T1 out1 62
3  G1    T2 out1 61
4  G2    T2 out1 62
5  G1    T1 out2 86
6  G2    T1 out2 64

Now, I add the sum within grp/treat to the dataframe (using sql, sorry!):

x0 <- sqldf(paste("SELECT a.*, (SELECT SUM(n)"
                  ,"            FROM x0 b"
                  ,"            WHERE a.grp = b.grp"
                  ,"                  AND a.treat = b.treat"
                  ,"           ) tot"
                  ," FROM x0 a"
                  ," ORDER BY a.grp,a.treat,a.out"
                  )
            )
x0$p <- with(x0, n/tot)
x0$p2 <- with(x0, paste(formatC(p*100, digits=2
              , format="fg"),"%",sep=""))
head(x0)
  grp treat  out  n tot          p    p2
1  G1    T1 out1 11 192 0.05729167  5.7%
2  G1    T1 out2 86 192 0.44791667   45%
3  G1    T1 out3 67 192 0.34895833   35%
4  G1    T1 out4 28 192 0.14583333   15%
5  G1    T2 out1 61 160 0.38125000   38%
6  G1    T2 out2  1 160 0.00625000 0.62%

And here is how I get the plot:

ggplot(x0, aes(grp, weight=n)) +
         geom_bar(aes(fill = out), position = "fill") +
         facet_grid(.~treat) +
         scale_y_continuous(labels=percent) +
         geom_text(aes(label=p2, y=p))

I could add a new variable to the dataframe with cumulative percentage but I'm wonder if there is a simpler way to add the labels.

Answer 1

To avoid creating the position values yourself, you can use position = "stack" in geom_text as in this question . As you noted in the comments, the dataset must be ordered by the fill variable to get the stacks in the correct order to match the bar stacks.

ggplot(x0, aes(grp, weight = n)) +
    geom_bar(aes(fill = out), position = "fill") +
    facet_grid(.~treat) +
    scale_y_continuous(labels=percent) +
    geom_text(aes(label = p2, y=p), position = "stack")

You may end up needing to remove the labels below a certain size to remove the overlap seen in the plot above. Something like geom_text(aes(label = ifelse(p < .05, NA, p2), y = p), position = "stack") would remove labels for the very small values.