[R] column wise paste of data.frames

[Sebastian Weber]

Hi everybody!

I'm sure that I overlook something and feel quite stupid to ask, but I
have not found an easy solution to the following problem: Take e.g. the
Orthodont data from the nlme package:

> head(Orthodont)
Grouped Data: distance ~ age | Subject
  distance age Subject  Sex
1     26.0   8     M01 Male
2     25.0  10     M01 Male
3     29.0  12     M01 Male
4     31.0  14     M01 Male
5     21.5   8     M02 Male
6     22.5  10     M02 Male

Suppose now, that I have a vector which contains the names of the
"meta"-fields in this data-frame:

metaFields <- c("Subject", "Sex")

I now would like to form a new column "ID" which consists of the columns
in metaFields joined like the following:

> head(Orthodont)
Grouped Data: distance ~ age | Subject
  distance age Subject  Sex  ID
1     26.0   8     M01 Male  M01/Male
2     25.0  10     M01 Male  M01/Male
3     29.0  12     M01 Male  M01/Male
4     31.0  14     M01 Male  M01/Male
5     21.5   8     M02 Male  M02/Male
6     22.5  10     M02 Male  M02/Male

Any paste commands I tried so far failed, e.g.:

Orthodont$ID <- paste(Orthodont[,metaFields], sep="/")

is simply wrong. Ok, I could add the columns within a loop to ID, but
that is not very elegant. Instead, what I need is a command that in
effect produces the output of

Orthodont$ID <- paste(Orthodont[,metaFields[1]],    
                      Orthodont[,metaFields[2]] , sep="/")

There should be some way to do it in R - can someone please enlighten
me? Thanks a lot in advance.

Greetings,

Sebastian