[R] data.frame preserves names for all columns

[Liaw, Andy]

Dear R-help,

I was surprised to find that data.frame() keeps the names of all columns:

> x1 <- structure(1:5, names=1:5)
> x2 <- structure(5:1, names=5:1)
> x3 <- structure(10:6, names=10:6)
> x <- data.frame(x1, x2, x3)
> str(x)
`data.frame':   5 obs. of  3 variables:
 $ x1: Named int  1 2 3 4 5
  ..- attr(*, "names")= chr  "1" "2" "3" "4" ...
 $ x2: Named int  5 4 3 2 1
  ..- attr(*, "names")= chr  "5" "4" "3" "2" ...
 $ x3: Named int  10 9 8 7 6
  ..- attr(*, "names")= chr  "10" "9" "8" "7" ...

I could not find mention of this in ?data.frame.  The problem is that when I
extract a column of `x', I would be expected the rownames of the data frame
to be used as the names (and short of that, no names attribute), rather than
the original names.  Is this intentional?

Best,
Andy

Andy Liaw, PhD
Biometrics Research      PO Box 2000, RY33-300     
Merck Research Labs           Rahway, NJ 07065
mailto:andy_liaw at merck.com <mailto:andy_liaw at merck.com>         732-594-0820