[Rd] Small change to plot.xy

[Jonathan Rougier]

OK -- so there are two objections to the proposal:

1) The factor might be a colour specifier

2) Using codes is not a good idea because there are only 8 colours
available for an integer argument to col.

I can see that both of these have merit, but I think they are both easy
to work around, if necessary.  No-one has disagreed that it's natural to
want to pass a factor to col, and I believe that the vast majority of
times when this occurs the factor is not designed explicitly to paint
the points.

I think I would let the first objection pass.  Using codes to coerce the
factor we still get different colours for different factors, just not
the specified colours.  This is not right, but it's rarely a disaster
either and should be easy to spot for anyone who is expecting to see
"slateblue" and gets "red".

As for the second objection, I think this is valid and should be
addressed, but at the same time it is a different problem.  I often
wondered why col = 1 was black (not really a colour at all, and not very
good for boxplots) and, more pertinently, why col = 2 is red and col = 3
is green: isn't the most common form of colour-blindness red/green?  At
the very least, let's not have them next to each other in the list!  We
have 657 named colours to choose from: why not have a explicit "int2col"
function that provides a bigger and better table?

More-or-less the same arguments also apply to pch.

Jonathan.

Jonathan Rougier wrote:
> 
> Hi everyone,
> 
> Is there any reason why we should not automatically coerce a factor
> supplied as an argument to col in a plotting function?  The following
> modification (to R-1.6.1) seems pretty harmless
> 
> > plot.xy
> function (xy, type, pch = 1, lty = "solid", col = par("fg"),
>     bg = NA, cex = 1, ...)
> {
>     if (is.factor(col))
>         col <- codes(col)
>     .Internal(plot.xy(xy, type, pch, lty, col, bg, cex, ...))
> }
> <environment: namespace:base>
> 
> and I think it is natural and not really wrong to want to type, say,
> 
> > data(iris)
> > pairs(iris[, 1:4], col = iris[, 5])
> 
> and get the colours.
> 
> Cheers, Jonathan.
> 
> --
> Jonathan Rougier                       Science Laboratories
> Department of Mathematical Sciences    South Road
> University of Durham                   Durham DH1 3LE
> tel: +44 (0)191 374 2361, fax: +44 (0)191 374 7388
> http://www.maths.dur.ac.uk/stats/people/jcr/jcr.html
> 
> ______________________________________________
> R-devel@stat.math.ethz.ch mailing list
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-- 
Jonathan Rougier                       Science Laboratories
Department of Mathematical Sciences    South Road
University of Durham                   Durham DH1 3LE
tel: +44 (0)191 374 2361, fax: +44 (0)191 374 7388
http://www.maths.dur.ac.uk/stats/people/jcr/jcr.html