From: Martin Maechler <maechler_at_stat.math.ethz.ch>

Date: Mon, 06 Feb 2012 15:35:36 +0100

R-devel_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-devel Received on Mon 06 Feb 2012 - 14:38:57 GMT

Date: Mon, 06 Feb 2012 15:35:36 +0100

> On Sat, Feb 4, 2012 at 10:38 AM, Martin Maechler

*> <maechler_at_stat.math.ethz.ch> wrote:
**> > The help has
**> >
**> >> Description:
**> >
**> >> 'nrow' and 'ncol' return the number of rows or columns present in 'x'.
**> >> 'NCOL' and 'NROW' do the same treating a vector as 1-column matrix.
**> >
**> > and
**> >
**> >> x: a vector, array or data frame
**> >
**> > I'm proposing to extend these two convenience functions
**> > to also work ``correctly'' for generalized versions of matrices.
**> >
**> >
**> > The current implementation :
**> >
**> > NROW <- function(x) if(is.array(x)||is.data.frame(x)) nrow(x) else length(x)
**> > NCOL <- function(x) if(is.array(x) && length(dim(x)) > 1L || is.data.frame(x)) ncol(x) else 1L
**> >
**> > only treats something as matrix when is.array(.) is true,
**> > which is not the case, e.g., for multiprecision matrices from
**> > package 'gmp' or for matrices from packages SparseM, Matrix or similar.
**> >
**> > Of course, all these packages could write methods for NROW, NCOL
**> > for their specific matrix class, but given that the current
**> > definition is so simple,
**> > I'd find it an unnecessary complication.
**> >
**> > Rather I propose the following new version
**> >
**> > NROW <- function(x) if(length(dim(x)) || is.data.frame(x)) nrow(x) else length(x)
**> > NCOL <- function(x) if(length(dim(x)) > 1L || is.data.frame(x)) ncol(x) else 1L
*

> DIM <- function(x) if (length(dim(x)) > 1L) dim(x) else c(length(x), 1L)

*> DIM <- function(x) {
*

> d <- dim(x)

*> if (length(d) > 1L) dim(x) else c(length(x), 1L)
**> }
*

> given that dim() is not always trivial to compute (e.g. for data

*> frames it can be rather slow if you're doing it for hundreds of data
**> frames)
*

> then NROW and NCOL could be exact equivalents to nrow and ncol.

> Hadley

Thank you, Hadley.

Indeed, your suggestion seems to make sense
{as far as it makes sense to have such simple functions to
exist in base at all, but as we already have NROW and NCOL ..}

So, I propose to adopt Hadley's DIM() proposal, modified to

DIM <- function(x) if(length(d <- dim(x))) d else c(length(x), 1L)

and wait a day or so (or longer for reasons of vacation!) before committing it, so the public can raise opinions.

Martin

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