Add "flow" to geom_bar

Question

I'm trying to plot the "flow" of individuals between two groups at certain timepoints.

In the following example:

d1=data.frame(c(1:6),
              c("A","B","A","A","B","A"),
              c("A","B","B","A","B","B")
              )

names(d1)=c("id","time1","time2")

require(reshape2)
m1=melt(d1,id.vars="id")

require(ggplot2)
ggplot(m1,aes(x=variable,fill=value))+
  geom_bar(stat="count",width = 0.5)

the individuals numbered 3 and 6 "switch" from group A to group B between observations "time1" and "time2". I am searching for a possibility to plot this. Tried geom_polygon but was not successful.

Here is what I like to get:
2 individuals staying in group A and 2 individuals switching to group 2.

A more complex example can be seen here: flow of voters between two elections.

[2] http://cdn1.salzburg24.at/2013/05/Waehlerstroeme-650x435.jpg

Is there a way to achieve this with ggplot?

Answer 1

Thanks aosmith!

This produced the result I expected:

require(alluvial)

d2=aggregate(d1[,2], 
             by= d1[, c('time1','time2')], 
             FUN=function(x) length(x))

names(d2)[3]="Freq"

alluvial(d2[,1:2],freq=d2$Freq)