Why does "^" on a data.frame return a matrix instead of a data.frame like "*" does?

Question

This question is motivated by a bug filed here by Abiel Reinhart on data.table. I noticed that the same happens on data.frame as well.

Here's an example:

DF <- data.frame(x=1:5, y=6:10) > DF*DF    x   y 1  1  36 2  4  49 3  9  64 4 16  81 5 25 100  > class(DF*DF) # [1] "data.frame"  > DF^2       x   y [1,]  1  36 [2,]  4  49 [3,]  9  64 [4,] 16  81 [5,] 25 100  > class(DF^2) # [1] "matrix" 

Why does "^" coerce it into a matrix? Any ideas? Note that ** is converted to ^ by the parser. So, doing DF**2 would give the same result as DF^2.

I don't find anything related to this coercion in ?`^`.

Edit: Neal's answer shows clearly the reason for ^ returning a matrix when operated on a data.frame. It'd be great if the question as to why ^ is being left out in that piece of code could be answered as well.

Edit 2: I also posted here on R-help and got a reply from Duncan that there seems to be no info reg. this change in the NEWS (admittedly, it's a quite old change as Joshua and Duncan also pointed out).

Answer 1

Ops.data.frame implements the math operators for data frames as S3 generics, here is the last couple lines:

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)) 

So ^ gets returned as a matrix.