>>>>> Hilmar Berger
>>>>> on Tue, 24 Sep 2019 19:31:51 +0200 writes:
> Dear Martin,
> thanks a lot for looking into this. Of course you were right that the
> fix was not complete - I apologize for not having tested what I believed
> to be the solution.
> My comments on the S4 classes seemed to stem from a misunderstanding on
> my side. I now believe to understand that S4 classes that inherit from R
> base object types might dispatch Ops for the same object types.
> If the base object value of such S4 classes is unset and therefore
> empty, this empty value will be passed on to e.g. Ops.data.frame where
> it would trigger the same issue as e.g. logical(0).
> setClass("MyClass", slots = list(x="numeric", label="character"),
> contains = "numeric")
> a = new("MyClass", x=3, label="FOO")
> a@.Data
>> logical(0)
> a == data.frame(a=1:3)
> # error
> I understand that this is all as expected and the error should most
> likely disappear with the fix you submitted for other 0-extent cases.
> Thanks again and best regards,
> Hilmar
You are welcome!
Indeed, I had modified code in R-devel that makes these Ops work with many
0-extent data frames (compatibly with corresponding 0-extent
matrices).
Thank you, Hilmar!
In addition I confirm that indeed comparison with S4 objects as
above now works too :
R Under development (unstable) (2019-09-23 r77210) -- "Unsuffered Consequences"
Copyright (C) 2019 The R Foundation for Statistical Computing
Platform: x86_64-pc-linux-gnu (64-bit)
## {learn: you can use the return value of setClass() !}
MY <- setClass("MyClass", slots = list(x="numeric",label="character"),
contains = "numeric")
a <- MY(x=pi, label="FOO")
D3 <- data.frame(a=1:3)
> identical(D3 == a, D3 == logical())
[1] TRUE
>
Best,
Martin
> Am 18/09/2019 um 11:29 schrieb Martin Maechler:
>>>>>>> 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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