Hi

With ggplot2 I can very easily create beautiful histograms but I would like to put two histograms on the same plot. The histograms may be over-lapping.
When they are overlapping the bars are shown on top of each other (so that the overall height is the sum of the two). Is there any way to get them to display overlapping (with smaller value in front, larger value behind) so that the overall height is equal to the height of the largest value

The following demonstrates the problem (there is probably a simple way to generate the sequence in d1 but I don't know it and just threw this together quickly)
d1<-c(1,2,2,3,3,3,4,4,4,4,5,5,5,5,5,6,6,6,6,7,7,7,8,8,9,6,7,7,8,8,8,9,9,9,9,10,10,10,10,10,11,11,11,11,12,12,12,13,13,14,15,15,16,16,16,17,17,17,17,18,18,18,18,18)

d2<-c(rep("a",25), rep("b",39))
dafr<-data.frame(d1,d2)

library(ggplot)
qplot(d1, data=dafr, fill=d2, geom='histogram', binwidth = 1)

Many thanks for any help
Sandy

Sandy Small
Clinical Physicist
NHS Forth Valley
and
NHS Greater Glasgow and Clyde


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