[Rd] Inconsistency between row and nrow

[Marc Schwartz]

Hi Gabor,

In strictly reading the help files for both nrow() and row(), the 'x' argument in the former case is "a vector, array, data frame, or NULL.", whereas in the latter case it is "a matrix-like object, that is one with a two-dimensional dim.".

Thus, I would expect row() to fail on a >= 3-dimensional array, as your example shows.

In reading the help file for slice.index(), there is the following in the See Also section:

"row and col for determining row and column indexes; in fact, these are special cases of slice.index corresponding to MARGIN equal to 1 and 2, respectively when x is a matrix."

further differentiating the behavior of row() and col() as more specific implementations in the 2-dimensional case.

To my read then, the difference in behavior appears to be intentional and expected.

Regards,

Marc Schwartz


-----Original Message-----
From: R-devel <r-devel-bounces using r-project.org <mailto:r-devel-bounces using r-project.org>> on behalf of Gabor Grothendieck <ggrothendieck using gmail.com <mailto:ggrothendieck using gmail.com>>
Date: Sunday, September 8, 2024 at 7:31 AM
To: "r-devel using r-project.org <mailto:r-devel using r-project.org>" <r-devel using r-project.org <mailto:r-devel using r-project.org>>
Subject: [Rd] Inconsistency between row and nrow


In the following nrow provides the expected result but row gives an
error. I would have thought that they would both work or both fail.


aa <- array(dim = 5:3)


nrow(aa)
## [1] 5


row(aa)
## Error in row(aa) : a matrix-like object is required as argument to 'row'


# this does work:
slice.index(aa, 1)


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