[Rd] Error message when calling t.test() and aov() with a factor variables

[Kurt Hornik]

>>>>> Viechtbauer, Wolfgang (NP) writes:

Thanks.  Patches welcome :-)

Best
-k

>> -----Original Message-----
>> From: Kurt Hornik <Kurt.Hornik using wu.ac.at>
>> Sent: Friday, October 11, 2024 14:18
>> To: Viechtbauer, Wolfgang (NP) <wolfgang.viechtbauer using maastrichtuniversity.nl>
>> Cc: r-devel <r-devel using r-project.org>
>> Subject: Re: [Rd] Error message when calling t.test() and aov() with a factor
>> variables
>> 
>> >>>>> Viechtbauer, Wolfgang (NP) writes:
>> 
>> > Hi all,
>> > Just noticed that the error that arises when calling t.test() with factors
>> could be a bit clearer:
>> 
>> >> t.test(factor(c(3,1,2,4,3,5,4,5)), factor(c(2,1,2,3,4,5)))
>> > Error in var(x) : Calling var(x) on a factor x is defunct.
>> >   Use something like 'all(duplicated(x)[-1L])' to test for a constant vector.
>> > In addition: Warning message:
>> > In mean.default(x) :
>> >   argument is not numeric or logical: returning NA
>> 
>> > Obviously, using factors as input is nonsense, but this might happen on
>> accident and then the error message could be a bit more on point. Similar for
>> aov():
>> 
>> >> aov(factor(c(3,1,2,4,3,5,4,5)) ~ factor(c(2,1,2,2,2,1,2,1)))
>> > Call:
>> >    aov(formula = factor(c(3, 1, 2, 4, 3, 5, 4, 5)) ~ factor(c(2,
>> >     1, 2, 2, 2, 1, 2, 1)))
>> > Error in levels(x)[x] :
>> >   only 0's may be mixed with negative subscripts
>> > In addition: Warning messages:
>> > 1: In model.response(mf, "numeric") :
>> >   using type = "numeric" with a factor response will be ignored
>> > 2: In Ops.factor(y, z$residuals) : '-' not meaningful for factors
>> 
>> > Not a big deal and trying to catch all of the silly things users may
>> > do is of course impossible, but for this one adding a check that the
>> > (response) variable is actually numeric could be useful.
>> 
>> Indeed.
>> 
>> As always, the question is whether we want to give an error unless
>> is.numeric, or ensure via as.numeric?

> I would issue an error. Using as.numeric() could lead to totally nonsensical results, for example when:

> as.numeric(factor(c("low","high","mid")))

>> Best
>> -k
>> 
>> > Best,
>> > Wolfgang