[R] Re: color coding a legend - solved?

[Prof Brian Ripley]

On Tue, 10 Jun 2003, Robert Schick wrote:

> I did the following, and had it plot as needed: 
> >legend(3.25, -2.5, leg.txt, pch=15, col= levels(as.factor(codes(cv.wshed.grp))))
> 
> Problem was in my (lack of) understanding of codes()

A common one.  codes() is deprecated in the development version of R, 
since it is much mis-used: indeed I could find no correct use in the R 
sources nor any of the packages I examined.

> But my second question is this: is there a way to color code the points
> on the first two PCA axes by group id within a biplot. Fig 11.7 in MASS
> 4 is my inspiration, but I don't understand how to use the col variable
> within biplot. The following works within a simple plot, but not a
> biplot:
> 
> >text(cv.mds.spr$points, labels = as.character(cv.wshed.id.spr), col = levels(as.factor(codes(cv.wshed.grp))), cex=.75)
> 
> Advice?

read the help page for biplot:

     col: A vector of length 2 giving the colours for the first and
          second set of points respectively (and the corresponding
          axes). If a single colour is specified it will be used for
          both sets.

A biplot both draws axes and plots points: there is no provision to 
suppress the plotting.   I'd start the other end, plotting the points as 
in MASS, then add the variable axes.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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