[R] Looping syntax?

Thomas Lumley tlumley at u.washington.edu
Fri Jun 29 20:05:49 CEST 2001

On Fri, 29 Jun 2001, Michaell Taylor wrote:

> Sorry for what I hope is an unchallenging question for R veterans.
> I have a question regarding looping syntax, though I know this should be
> avoided if possible in R - as in most other stat languages with which I am
> familiar.
> I would like to perform a series of operations on the subsets as defined by
> condition. Given the following data frame
> condition	X 	Y
> aa		4	5
> aa		8	9
> .
> .
> bb		8	4
> bb		3 	9
> .
> .
> more ..
> There are over 100 condition states, each with several hundred observations.
> For ease of this example, lets assume that I wish to make XY plots of each of
> the 100 condition states, with In other words, I need a structure like the
> following

I think you want something like

for(state in unique(condition)){
	these<-condition %in% state
		main=paste("Condition is",state))

The loop could be replaced with sapply(), but I would expect that the file
access would be the rate-limiting step so sapply() wouldn't help a lot.
The whole thing could also be done with tapply() or by(). This is left as
an exercise for the reader.


Thomas Lumley			Asst. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle

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