[Rd] simplify2array assumes non-NA dim() -- base or method bug?

Sebastian Meyer @eb@meyer @end|ng |rom |@u@de
Thu Aug 25 11:55:24 CEST 2022

Hmm. I think I haven't seen NA dims in base R before. R-lang says

> The 'dim' attribute is used to implement arrays.  The content of
> the array is stored in a vector in column-major order and the 'dim'
> attribute is a vector of integers specifying the respective extents of
> the array.  R ensures that the length of the vector is the product of
> the lengths of the dimensions.

And R-intro says:

> A dimension vector is a vector of non-negative integers.

I understand "vector of [non-negative] integers" as excluding NA_integer_.


> a <- 1
> dim(a) <- NA_integer_

Error in dim(a) <- NA_integer_ : the dims contain missing values

> matrix(1, NA_integer_)

Error in matrix(1, NA_integer_) : invalid 'nrow' value (too large or NA)

> array(1, NA_integer_)

Error in array(1, NA_integer_) : negative length vectors are not allowed

There must be many more examples where non-NULL dim() is assumed to
not contain missing values.

simplify2array() aligns with that specification and only needs to check
for numeric (non-NULL) dims at this point and not also !anyNA(c.dim).
So my take is that there is no bug.

Best regards,

	Sebastian Meyer

Am 25.08.22 um 04:51 schrieb Michael Chirico via R-devel:
> If any component of the dim() returned as c.dim here[1] are missing,
> simplify2array() errors inscrutably (specifically, because the last &&
> condition is missing):
> Error in if (higher && length(c.dim <- unique(lapply(x, dim))) == 1 &&  :
>    missing value where TRUE/FALSE needed
> At root here is that dim.tbl_lazy ({dbplyr} package method [2]) very
> intentionally neglects to count the # of rows in the result -- the
> whole point of a lazy table is to avoid calculating full queries
> unless specifically requested, so the # of rows is left as missing,
> i.e., there _is_ a quantity of rows, but the exact number is not
> known.
> That seems to me like a proper usage of NA, and hence this is a
> simplify2array() bug, but I am curious other thoughts here before
> attempting a patch.
> [1] https://github.com/r-devel/r-svn/blob/2d4f8c283d53ff2c98d92c7b77b11e652297742c/src/library/base/R/sapply.R#L46-L48
> [2] https://github.com/tidyverse/dbplyr/blob/36b146e36d6d9af215dc48e60862d4b807b9e606/R/tbl-lazy.R#L45-L47
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