ggplot2: group x axis discrete values into subgroups

Question

I would like to create a bar plot with ggplot2 in which the discrete values of the x axis would be grouped into subgroups (see picture attached - the picture is from the web I do not have a code for the plot yet).

Thanks for your help !

Solution

Two approaches:

Example data:

dat <- data.frame(value=runif(26)*10,
                  grouping=c(rep("Group 1",10),
                             rep("Group 2",10),
                             rep("Group 3",6)),
                  letters=LETTERS[1:26])

head(dat)
     value grouping letters
1 8.316451  Group 1       A
2 9.768578  Group 1       B
3 4.896294  Group 1       C
4 2.004545  Group 1       D
5 4.905058  Group 1       E
6 8.997713  Group 1       F

Without facetting:

ggplot(dat, aes(grouping, value, fill=letters, label = letters)) + 
     geom_bar(position="dodge", stat="identity") + 
     geom_text(position = position_dodge(width = 1), aes(x=grouping, y=0))

With facetting:

ggplot(dat, aes(letters,value, label = letters)) + 
     geom_bar(stat="identity") + 
     facet_wrap(~grouping, scales="free")

Facetting has the obvious advantage of not having to muck about with the positioning of the labels.

Comments

[lqdo2000]

Thanks ! It looks pretty good with facetting. However, is it possible to get the same width for all the bars independently of the numbers of values I have for each group?(when using scales="free_x", the width of the groups is the same but not the bars. When using scales="free_y", that's the opposite).

[lqdo2000]

Found it. I used facet_grid with the argument 'space="free_x"` !

[Katie S]

How would you do this on the y axis with discrete, non-numberical values ?