[R] combn with factors

[Greg Hirson]

Dear list,

I have come across this issue:

combn(letters[1:5], 3)

      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,] "a"  "a"  "a"  "a"  "a"  "a"  "b"  "b"  "b"  "c"
[2,] "b"  "b"  "b"  "c"  "c"  "d"  "c"  "c"  "d"  "d"
[3,] "c"  "d"  "e"  "d"  "e"  "e"  "d"  "e"  "e"  "e"

combn(factor(letters[1:5]), 3)

      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,] "a"  "1"  "1"  "1"  "1"  "1"  "2"  "2"  "2"  "3"
[2,] "b"  "2"  "2"  "3"  "3"  "4"  "3"  "3"  "4"  "4"
[3,] "c"  "4"  "5"  "4"  "5"  "5"  "4"  "5"  "5"  "5"

I'm not sure why the first combination uses the factor labels and the 
remaining combinations use the factor value. In the second case, I 
expected that the labels would be used. In any event, I think it could 
be consistent - either labels or values.

Is there reason to expect the second case to return the value it did?

This occurs in R 2.10.1

Thanks,
Greg

-- 
Greg Hirson
ghirson at ucdavis.edu

Graduate Student
Agricultural and Environmental Chemistry

1106 Robert Mondavi Institute North
One Shields Avenue
Davis, CA 95616