Reorder legend without changing order of points on plot

Question

I keep running into this issue in ggplot2, perhaps someone can help me.

I have a plot where the order of the variables in the legend is in reverse order to how they are displayed on the plot.

For example:

df=data.frame(
 mean=runif(9,2,3),
 Cat1=rep(c("A","B","C"),3),
 Cat2=rep(c("X","Y","Z"),each=3))

dodge=position_dodge(width=1)
ggplot(df,aes(x=Cat1,y=mean,color=Cat2))+
 geom_point(aes(shape=Cat2),size=4,position=dodge)+
 scale_color_manual(values=c("red","blue","black"))+
 scale_shape_manual(values=c(16:19))+
 coord_flip()

produces:

So the points are displayed on the plot as Cat2=Z,Y, then X (black diamonds, blue triangle, red circle) but in the legend they are displayed as Cat2=X, Y, then Z (red circle, blue triangle, black diamond).

How can I reverse the order of the legend without shifting the points on the plot? Reordering the factor produces the opposite problem (points on the plot are reversed).

Thanks!

Answer 1

To flesh out Hadley's comment, we would do something like this:

ggplot(df,aes(x=Cat1,y=mean,color=Cat2))+
 geom_point(aes(shape=Cat2),size=4,position=dodge)+
 scale_color_manual(values=c("red","blue","black"),breaks = c('Z','Y','X'))+
 scale_shape_manual(values=c(16:19),breaks = c('Z','Y','X'))+
 coord_flip()

Note that we had to set the breaks in both scales. If we did just one, they wouldn't match, and ggplot would split them into two legends, rather than merging them.