Great! I got it. You're right, I misinterpreted Duncan's suggestion.
Thanks a lot to both of you...

Matteo

On 24 November 2011 02:47, Rolf Turner-3 [via R]
<ml-node+s789695n4102338h14@n4.nabble.com> wrote:
> On 24/11/11 09:23, matric wrote:
>> Thanks Duncan,
>> I knew it. But if I use the complete variable name, I'll have far too
>> many arguments for my function....
>
> Did you understand Duncan's post?  He told you that
>
>      df[,var]
>
> would work, whereas df$var doesn't.  So he gave you a solution
> to the problem whereby you ***don't*** have to use the ``complete
> variable name''.
>
> The ``var'' in the foregoing is the object (character string) that you
> constructed using paste().  I think you are misinterpreting Duncan
> to be suggesting that you use df[,"x_narrow"], df[,"x_wide"] etc.
> explicitly.
>
>      cheers,
>
>          Rolf Turner
>
> P. S.  But anyway, as Duncan said in a follow-up post, a new design is
> probably
> called for.
>
>          R. T.
>> On 23 November 2011 20:59, Duncan Murdoch-2 [via R]
>> <[hidden email]>  wrote:
>>> On 23/11/2011 2:29 PM, matric wrote:
>>>> Hi,
>>>> I'd like to create a function that accepts as arguments a string that is
>>>> to
>>>> be substituted within a variable name. For instance, suppose I have a
>>>> data
>>>> frame df:
>>>>
>>>> df<-data.frame(x_narrow=c(rnorm(100,0,1)),x_wide=c(rnorm(100,0,10)))
>>>>
>>>> What I have in mind is something like:
>>>>
>>>> f<- function(string){
>>>> var = paste("x_",string,sep = "")
>>>> df$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
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