[R] Multiple colors in plots/lookup function

John Fox jfox at mcmaster.ca
Thu Oct 17 13:28:42 CEST 2002

Dear David,

At 12:04 AM 10/17/2002 -0400, David Forrest wrote:

>   I'd like to do something like:
>  n<-100
>  zz<-cbind(rnorm(n),rnorm(n),floor(runif(n)*3+1))
>  colors<-c("red","green","blue")
>  plot(zz,col=colors(zz[3]))
>and have a matrix of scatterplots colored by class.  The above does not
>work, of course, but I'm not sure exactly what function I'm looking for.

A couple of people have already mentioned that specifying 
col=colors[zz[,3]] will colour the points in a scatterplot (not a 
scatterplot matrix) by the values of zz[,3]. Since there are just two other 
columns (the third column of zz is ignored in the first argument to plot), 
you get a scatterplot, not a scatterplot matrix, and it's hard to see how a 
scatterplot matrix would be relevant.

If, however, you want a scatterplot matrix of pairwise plots for three or 
more variables coloured by the levels of a factor, the scatterplot.matrix 
function in the car package should do what you want.


John Fox
Department of Sociology
McMaster University
Hamilton, Ontario, Canada L8S 4M4
email: jfox at mcmaster.ca
phone: 905-525-9140x23604
web: www.socsci.mcmaster.ca/jfox

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