Setting user colors in barchart

Thank you for a clear example, it works. I tried to play with 
superpose.polygon before to no avail, this clarifies things.

You're welcome.

Another question: would you know how to add gridlines to the plot? 
I'd like to have a few horizontal gridlines on my barchart plot for 
better readability. Do I have to write a wrapper for panel.barchart?

Probably, but it's not as bad as it sounds.  To reuse the previous 
example:

barchart(yield ~ site,
  groups=variety,
  data = barley,
  panel=function(...){panel.barchart(...); panel.grid(v=0, ...)})

(The v=0 argument stop vertical grid lines being drawn.)

Regards,
Richie.

Mathematical Sciences Unit
HSL


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