Re: [R] Using string vectors as for loop arguments

From: Berton Gunter <>
Date: Sat 04 Feb 2006 - 08:53:57 EST


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.

> -----Original Message-----
> From:
> [] On Behalf Of Kevin Middleton
> Sent: Friday, February 03, 2006 1:41 PM
> To:
> 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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> mailing list PLEASE do read the posting guide! Received on Sat Feb 04 09:09:29 2006

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