Arunkumar Srinivasan
2013-Nov-13 23:00 UTC
[R] On "^" returning a matrix when operated on a data.frame
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. Please let me know if I should be posting this to R-devel list instead. Thank you very much, Arun [[alternative HTML version deleted]]
Duncan Murdoch
2013-Nov-13 23:32 UTC
[R] On "^" returning a matrix when operated on a data.frame
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 > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >