[R] Multiple colors in plots/lookup function
John Fox
jfox at mcmaster.ca
Thu Oct 17 17:34:05 CEST 2002
Dear Martin,
At 03:21 PM 10/17/2002 +0200, Martin Maechler wrote:
> >>>>> "John" == John Fox <jfox at mcmaster.ca>
> >>>>> on Thu, 17 Oct 2002 07:28:42 -0400 writes:
>
> John> Dear David, At 12:04 AM 10/17/2002 -0400, David
> John> 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.
>
> John> A couple of people have already mentioned that
> John> specifying col=colors[zz[,3]] will colour the points
> John> in a scatterplot (not a scatterplot matrix) by the
> John> values of zz[,3].
>
>yes, even in a scatterplot matrix.
>Try a very slight variation of the above :
>
> n <- 100
> zz <- data.frame(Z1 = rnorm(n), Z2 = rnorm(n), Ufact = floor(runif(n)*3+1))
> colors <- c("red","green","blue")
> plot(zz, col = colors[zz[, 3]])
>
>i.e., the only practical difference is that I used
>data.frame() instead of
>cbind()
>
>--> which changes things: The plot() method for a data.frame calls
>pairs() which *is* the same as a scatterplot matrix.
>
> John> Since there are just two other
> John> columns (the third column of zz is ignored in the
> John> first argument to plot), you get a scatterplot, not a
> John> scatterplot matrix, and it's hard to see how a
> John> scatterplot matrix would be relevant.
>
>indeed!
>
> John> If, however, you want a scatterplot matrix of pairwise
> John> plots for three or more variables coloured by the
> John> levels of a factor, the scatterplot.matrix function in
> John> the car package should do what you want.
>
>I don't see why pairs() {or as mentioned, plot( ) for a data.frame}
>shouldn't be sufficient.
Actually, scatterplot.matrix calls pairs; it just makes it simpler (in my
opinion) to get a graph with features like points plotted with different
colours and symbols, a legend, univariate displays down the main diagonal,
concentration ellipses, regression lines, etc.
Regards,
John
-----------------------------------------------------
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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