>>>>> Martin Maechler
>>>>> on Wed, 18 Sep 2019 10:35:42 +0200 writes:
>>>>> Hilmar Berger
>>>>> on Sat, 14 Sep 2019 13:31:27 +0200 writes:
>> Dear all,
>> I did some more tests regarding the == operator in Ops.data.frame
(see
>> below). All tests done in R 3.6.1 (x86_64-w64-mingw32).
>> I find that errors are thrown also when comparing a zero length
>> data.frame to atomic objects with length>0 which should be a valid
case
>> according to the documentation. This can be traced to a check in the
>> last line of Ops.data.frame which tests for the presence of an empty
>> result value (i.e. list() ) but does not handle a list of empty
values
>> (i.e. list(logical(0))) which in fact is generated in those cases.
>> There is a simple fix (see also below).
> I'm pretty sure what you write above is wrong: For some reason
> you must have changed more in your own version of Ops.data.frame :
> Because there's a line
> value <- unlist(value, ...)
> there, value is *not* list(logical(0)) there, but rather logical(0)
> and then indeed, your proposed line change (at the end of Ops.data.frame)
> has no effect for the examples you give.
On the other hand, there *is* a simple "fix" at the end of
Ops.data.frame() which makes all your examples "work" (i.e. not
give an error), namely
----------------------------------------------------------------------
@@ -1685,7 +1684,7 @@
else { ## 'Logic' ("&","|") and 'Compare' ("==",">","<","!=","<=",">=") :
value <- unlist(value, recursive = FALSE, use.names = FALSE)
matrix(if(is.null(value)) logical() else value,
- nrow = nr, dimnames = list(rn,cn))
+ nrow = nr, ncol = length(cn), dimnames = list(rn,cn))
}
----------------------------------------------------------------------
i.e., explicitly specifying 'ncol' compatibly with the column names.
However, I guess that this change would *not* signal errors
where it *should* and so am *not* (yet?) proposing to "do" it.
Another remark, on S4 which you've raised several times:
As you may know that the 'Matrix' package (part of every
"regular" R installation) uses S4 "everywhere" and it does
define many methods for its Matrix classes, all in source file Matrix/R/Ops.R
the development version (in svn / subversion) being online on R-forge here:
https://r-forge.r-project.org/scm/viewvc.php/pkg/Matrix/R/Ops.R?view=markup&root=matrix
and "of course", there we define S4 group methods for Ops all
the time, and (almost) never S3 ones...
[[but I hope you don't want to start combining data frames
with Matrix package matrices, now !]]
Martin Maechler
ETH Zurich and R Core Team
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