Use paste function to select column of data

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Hello,

I want to build a function to call up a column of a data.frame by the names of the columns.  I have column names that are sequentially named (col1, col2, etc.). How do I change a character expression into something that will be understood as a data.frame column.  For example:

  example<-data.frame(cbind(col1=1:10, col2=21:30, col3=41:50))
   call.fun<-function(t){
     x<-paste("col",t, sep="")  ## Change this so that it is the data, not a character expression
      example$x}

call.fun(t=2)
Get out of the dollar habit.
Replace your

   example$x

with

   example[[x]]

or with

   example[, x]

Peter Ehlers
  Within the real function, I will continue do calculations on the column of data.  My problem is that I am either getting a character expression or NULL from my function.

Thanks for your help on what is probably a very simple question.

John
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Hello,

I want to build a function to call up a column of a data.frame by  
the names of the columns.  I have column names that are sequentially  
named (col1, col2, etc.). How do I change a character expression  
into something that will be understood as a data.frame column.  For  
example:

example<-data.frame(cbind(col1=1:10, col2=21:30, col3=41:50))
 call.fun<-function(t){
   x<-paste("col",t, sep="")  ## Change this so that it is the data,  
not a character expression
# right.... don't use the "$" operator, instead  use "[["
         example[[x]]    }
call.fun(t=2)

Within the real function, I will continue do calculations on the  
column of data.  My problem is that I am either getting a character  
expression or NULL from my function.

Thanks for your help on what is probably a very simple question.

John

David Winsemius, MD
Heritage Laboratories
West Hartford, CT