Removing "row.names"

Thomas Lumley writes:

On Wed, 7 Feb 2001, Kurt Hornik wrote:

Thomas Lumley writes:

On Wed, 7 Feb 2001, Kurt Hornik wrote:

Peter Dalgaard BSA writes:

Kurt Hornik <Kurt.Hornik@ci.tuwien.ac.at> writes:

names(sampled) <- " "
and
dimnames(sampled)[[2]] <- " "

happily introduce non-unique variable names in the data frame.

Is the rule that row.names and names must be unique still on?

Argh ...

Splus 3.4 dispatches on dimnames<-, but not on names<- with the
following curious result:

d <- data.frame(a=1:3,b=4:6)
names(d)<-c(" "," ")
d

1 1 4
2 2 5
3 3 6

dimnames(d)[[1]] <- rep(" ",3)  

Error in "dimnames<-.data.frame"(d, .A0): column names must be unique
Dumped

R dispatches similarly, but doesn't check the dimnames in
dimnames<-.data.frame. It could do so quite easily. Just add 

|| any(duplicated(d[[1]])) || any(duplicated(d[[2]]))

at the appropriate spot.

Thomas' view about what should be permitted seems to be different.

I wouldn't object to making it hard to create duplicated names(), but
I think it would be a bad idea to have data.frame() make up unique
names if it's given non-unique ones.

Maybe `check.names' could also be used for uniqueness testing?

In any case, I think we should specify what *exactly* a data frame is.

I think we should specify, and check.names is a logical way to
allow/forbid non-unique columns.

Having a new class would be messy: logically it shouldn't inherit from
data.frame, data.frame should inherit from it, but that would be a real
pain to set up.