R help - Nov 2011 - character substitution within a variable name

Hi,
I'd like to create a function that accepts as arguments a string that is to
be substituted within a variable name. For instance, suppose I have a data
frame df:

df<-data.frame(x_narrow=c(rnorm(100,0,1)),x_wide=c(rnorm(100,0,10)))

What I have in mind is something like:

f <- function(string){
var = paste("x_",string,sep = "")
df$var
}

which does not work. Any suggestion for modifications? Thanks in advance,
Matteo

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On 23/11/2011 2:29 PM, matric wrote:
> Hi,
> I'd like to create a function that accepts as arguments a string that
is to
> be substituted within a variable name. For instance, suppose I have a data
> frame df:
>
> df<-data.frame(x_narrow=c(rnorm(100,0,1)),x_wide=c(rnorm(100,0,10)))
>
> What I have in mind is something like:
>
> f<- function(string){
> var = paste("x_",string,sep = "")
> df$var
> }
>
> which does not work. Any suggestion for modifications? Thanks in advance,
For indexing a dataframe, use the name as the column index:

df[, var]

will work.

Duncan Murdoch