[External] Re: R C API resize matrix
On Mon, 17 Jun 2019, Simon Urbanek wrote:
Matrix is just a vector with the dim attribute. Assuming it is not referenced by anyone, you can set any values to the dim attribute. As for the vector, you can use SET_LENGTH() to shorten it - but I'm not sure how official it is - it was originally designed to work, but there were abuses of TRUELENGTH so not sure where we stand now (shortened vectors used to fool the garbage collector as far as object sizes go). I wouldn't do it unless you're dealing with rally huge matrices.
Don't do that. SET_LENGTH isn't part of the API and using it outside specific internal code confuses the garbage collector. There is support for a growable vector but it's not a at a point where the interface is stable enough to be used in packages. So again please don't go there. Also for a matrix unless you are just dropping trailing columns you would have to move data in memory. Best, luke
Cheers, Simon
On Jun 14, 2019, at 5:31 PM, Morgan Morgan <morgan.emailbox at gmail.com> wrote: Hi, Is there a way to resize a matrix defined as follows: SEXP a = PROTECT(allocMatrix(INTSXP, 10, 2)); int *pa = INTEGER(a) To row = 5 and col = 1 or do I have to allocate a second matrix "b" with pointer *pb and do a "for" loop to transfer the value of a to b? Thank you Best regards Morgan [[alternative HTML version deleted]]
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Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
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