?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 > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! > http://www.R-project.org/posting-guide.html > ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html