How to move or position a legend in ggplot2

Question

I'm trying to create a ggplot2 plot with the legend beneath the plot.

The ggplot2 book says on p 112 "The position and justification of legends are controlled by the theme setting legend.position, and the value can be right, left, top, bottom, none (no legend), or a numeric position".

The following code works (since "right" it is the default), and it also works with "none" as the legend position, but "left", "top", "bottom", all fail with "Error in grid.Call.graphics("L_setviewport", pvp, TRUE) : Non-finite location and/or size for viewport"

library(ggplot2)
(myDat <- data.frame(cbind(VarX=10:1, VarY=runif(10)), 
    Descrip=sample(LETTERS[1:3], 10, replace=TRUE)))
qplot(VarX,VarY, data=myDat, shape=Descrip) + 
    opts(legend.position="right")

What am I doing wrong? Re-positioning a legend must be incredibly common, so I figure it's me.

Answer 1

In versions > 0.9.3 (when opts was deprecated)

theme(legend.position = "bottom")

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Older version:

Unfortunately it's a bug in ggplot2 which I really really hope to fix this summer.

Update:

The bug involving opts(legend.position = "left") has been fixed using the most current version of ggplot2. In addition, version 0.9.0 saw the introduction of guide_legend and guide_colorbar which allow much finer control over the appearance and positioning of items within the legend itself. For instance, the ability specify the number of rows and columns for the legend items.