[R] Using string vectors as for loop arguments

[Kevin Middleton]

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