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

Given your function definition, the function call needs to be

x(c("age","day"))

Whether it is good form to write a function like this, I will leave to others to comment.