[R] On "^" returning a matrix when operated on a data.frame

[Duncan Murdoch]

On 13-11-13 6:00 PM, Arunkumar Srinivasan wrote:
> Dear R-users,
>
> I am wondering why "^" operator alone returns a matrix, when operated on a data.frame (as opposed to all other arithmetic operators). Here's an example:
>
> DF <- data.frame(x=1:5, y=6:10)
> class(DF*DF) # [1] data.frame
> class(DF^2) # [1] matrix
>
> I posted here on SO: http://stackoverflow.com/questions/19964897/why-does-on-a-data-frame-return-a-matrix-instead-of-a-data-frame-like-do and got a very nice answer - it happens because a matrix is returned (obvious by looking at `Ops.data.frame`). However, what I'd like to understand is, *why* a matrix is returned for "^" alone? Here's an excerpt from Ops.data.frame (Thanks to Neal Fultz):
>
> if (.Generic %in% c("+", "-", "*", "/", "%%", "%/%")) {
>      names(value) <- cn
>      data.frame(value, row.names = rn, check.names = FALSE,
>          check.rows = FALSE)
> }
> else matrix(unlist(value, recursive = FALSE, use.names = FALSE),
>      nrow = nr, dimnames = list(rn, cn))
>
>
> It's clear that a matrix will be returned unless `.Generic` is one of those arithmetic operators. My question therefore is, is there any particular reason why "^" operator is being missed in the if-statement here? I can't think of a reason where this would break. Also ?`^` doesn't seem to mention anything about this coercion.

It's not just ^ that is missing, the logical relations like <, ==, etc 
also return matrices.  This is very old code (I think from 1999), but I 
would guess that the reason is that the ^ and < operators always return 
values of a single type (numeric and logical respectively), whereas the 
other operators can take mixed type inputs and return mixed type outputs.

Duncan Murdoch

> Please let me know if I should be posting this to R-devel list instead.
>
> Thank you very much,
> Arun
>
>
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