Richard,

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

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?

Thanks
Alex

On Tue, Sep 16, 2008 at 10:49 AM, <Richard.Cotton@hsl.gov.uk> wrote:

> > I have a basis question regarding the use of color in the lattice
> package. I
> > read the ?barchart help page and searched the R archives but could not
> > understand how to do it.
> >
> > I just need to plot a barchart using specific colors for my groups, e.g.
> > green and red instead of the default lattice colors. How do I do that?
> >
> > If I say:
> >     barchart(x ~ a_factor, groups=my_groups, data=my_data,
> col=c('green',
> > 'red'), auto.key=TRUE)
> >
> > then my barplot has the correct colors, but the legend does not. What is
> the
> > correct approach to set colors in barchart?
>
> Two possibilities:
> 1. Manually specify the colours of the rectangles in the key by using the
> key argument instead of auto.key
>
> my_cols <- c("green", "red", "blue")
> barchart(yield ~ site,
>   groups=variety,
>   data = barley,
>   col=my_cols,
>   key=list(text=list(levels(barley$variety)),
> rectangles=list(col=my_cols)))
>
> 2. Set superpose.polygon$col in the plot settings instead of using the col
> argument, e.g.
>
> barchart(yield ~ site,
>   groups=variety,
>   data = barley,
>   auto.key=TRUE,
>   par.settings=list(superpose.polygon=list(col=my_cols)))
>
> Regards,
> Richie.
>
> Mathematical Sciences Unit
> HSL
>
>
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