[R] Transparent colors OR two series on one histogram

[Thomas Lumley]

On Thu, 10 Mar 2005, Nathaniel Street wrote:

> Hi,
>
> I want to be able to plot a single histogram of a measured trait with trait 
> values from two conditions on the same histogram to allow easy comparison.
>
> I have previously done this in excel by plotting the two series on a single 
> bargraph having calculated frequencies in bins. You then get one condition 
> plotted immediately to the right of the other. I hope that makes sense?
>
> I don't know if this is possible in R?

You can do it for bar plots, but not for histograms.  Look at 
barplot(beside=TRUE)

> If not, I could plot the second one on top of the first i.e.
>
> hist(x)
> hist(y,add=TRUE)
>
> but i would need to set one as having a semi-transparent color so that where 
> the two sets of are plotted on top of each other, you can see the frequency 
> of the first series 'behind' the second.

Semitransparent colors are available for the pdf() and quartz() devices. 
They were described by Paul Murrell in R News Vol 4 No 2.

 	-thomas