[R] Can this be vectorized?

Marc Feldesman feldesmanm at pdx.edu
Tue May 1 17:50:35 CEST 2001


I want to produce some boxplots (and qqnorm plots) for each of a series of 
groups.  It is easy to produce the boxplots or qqplots by groups using 
either by() or tapply(), but the moment that I want unique labels for each 
boxplot, I seem to be stuck using a for loop to achieve the effect.

For example:

tapply(fstat$femur, fstat$race, boxplot)
by(fstat$femur, fstat$race, boxplot)

gives nicely unlabelled boxplots.

but I'm struggling with how to pass the labelling arguments to either 
tapply or by:

e.g.

tapply(fstat$femur, fstat$race, function(x) boxplot(x, main=????))

(nothing obvious comes to mind here that extracts the levels of fstat$race

but:

for (i in 1:3) {
boxplot(fstat[as.numeric(fstat$race)==i, "femur"], main=levels(fstat$race)[i])
}

gives exactly what I want.

It probably isn't worth the effort to avoid the loop above, but curiosity 
compels me to ask whether there is a way to vectorize the extraction of the 
levels from within an apply, tapply, by....?

Thanks.




=====================
Dr. Marc R. Feldesman
Professor and Chairman
Anthropology Department
Portland State University
1721 SW Broadway
Portland, Oregon 97201
email:  feldesmanm at pdx.edu
phone:  503-725-3081
fax:    503-725-3905
http://web.pdx.edu/~h1mf
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======================

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If we're looking for the source of our troubles, we shouldn't test people
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