Duncan: I must humbly disagree. Here's the problem: in order to accurately represent the value, the "point" = circle _area_ must be proportional to the value. That is, the eye "sees" the areas, not the radii, as the point "size." A delightful reference on this is Howard Wainer's 1982 or so (can't remember exactly) article in THE AMERICAN STATISTICIAN, "How to Graph Data Badly" (or maybe "Plot" Data).
Anyway, using cex, I have no idea whether a point drawn with cex = 1.23 is 1.23 times the area or radius -- or neither -- of a point drawn with cex =1. Indeed, it might vary depending on the implementation/OS/graphics fonts. So it seems better to me to "draw" the point with symbols(), where you can have complete control over the size. Obviously, let me know if I'm wrong about this. Cheers, Bert On Wed, Jan 12, 2011 at 9:11 PM, Duncan Murdoch <murdoch.dun...@gmail.com> wrote: > On 11-01-12 9:33 PM, John Sorkin wrote: >> I would like to plot 3-dimensional data on a two-dimensional scatter-plot. >> Is there a way I can automatically modify the plot symbol (e.g. changing >> size or color) to indicate the value of a third variable? E.g. How can I >> plot weight vs. age and indicate the value of muscle mass for each value >> weight-age pair by making the plot point proportional to the subject's >> muscle mass? > > Just set cex to the other variable. For example, > > plot(1:10, 1:10, cex=1:10) > > Similarly, col and pch can be set to vector values, which are recycled > through the points. > > Duncan Murdoch > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- Bert Gunter Genentech Nonclinical Biostatistics 467-7374 http://devo.gene.com/groups/devo/depts/ncb/home.shtml ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
