subset select="variable with a list of names"

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
project.org] On Behalf Of Francisco
Sent: Thursday, February 09, 2012 4:52 AM
To: r-help at r-project.org
Subject: [R] subset select="variable with a list of names"

Hello,
I would like to make a function which extracts a subset, from a
dataset,
with only the columns that I want (specifying their names).

For example, having this matrix:

 > mydata<-matrix(c(22,1,3,2001,24,5,7,2002,26,7,8,2002,28,5,7,2003),

byrow=TRUE, ncol=4, dimnames=list(c(1,2,3,4),
c("age","day","month","year")))

 > mydata

   age day month year
1  22   1     3 2001
2  24   5     7 2002
3  26   7     8 2002
4  28   5     7 2003


I would like to create a function like:
x<-function(names) {subset(mydata, select=names) }

So I can choose every time which columns select, i.e. when I call:
x("age,day")

it would returns:
   age day
1  22   1
2  24   5
3  26   7
4  28   5

Obviously it is not working, and I don't know how to do to fix it. Do
you have any suggestion?

Thank you very much