[R] histogram in the background?

[hadley wickham]

> I intend to draw a plot of y against x. In the background of this graph I
> wish to creat a histogram of the horizontal variable x. Does any expert know
> how to produce such a plot?

When constructing such a plot, you need to be careful that you don't
end up constructing a pretty picture instead of a statistical graphic.
 In this case you need to ask yourself, what would the y-axis
represent?  What scale would it have?

Hadley