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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