?apply
as in:
answer-apply(yourframe,2,function(x)x[EXP==1 DOSE==1])
Note that there are slicker ways to do this call.
Note also for that for the particular case of column means, you have a
built-in much faster alternative:
answer-colMeans(yourframe[EXP==1 DOSE==1,],na.rm=TRUE)
Also note that the == construction may be problematic if EXP or DOSE are not
factors, say.
Finally, you need to start reading the R docs to learn about this yourself.
An Introduction to R is a good place to start.
Oh... and your attempt below will certainly not work. After you read the
basic docs, you'll see why not.
-- Bert Gunter
Genentech Non-Clinical Statistics
South San Francisco, CA
-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Kevin Middleton
Sent: Friday, February 03, 2006 1:41 PM
To: r-help@stat.math.ethz.ch
Subject: [R] Using string vectors as for loop arguments
Is there a mechanism to interate through a vector of strings? Say I
have a data frame of 50 variables (VAR1 to VAR50), each with 100
measurements along with some coding factors (EXP and DOSE). I
want to
calculate the mean of a subset of each of VAR1 to VAR 50 (selecting
by EXP and DOSE). Rather than just copy/pasting the same code 50
times, I thought of using a for loop to go through a vector of VAR1
to VAR50 (VAR.LIST below). Each iteration would be the variable name
for which the mean would be calculated.
Trying this, I get an error that the argument is not numeric or
logical. So I assume that for loops with vectors of strings are
disallowed. What I am wondering is whether there a way to mimic this
sort of procedure?
The code looked something like this:
VAR.LIST-paste(c(VAR), 1:50, sep=)
for (i in VAR.LIST){
mean(i[EXP==1 DOSE==1], na.rm=T)
}
Thanks
Kevin Middleton
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