[R] Data frame vs matrix quirk: Hinky error message?

[Bert Gunter]

Many thanks, Ista:

I only looked in "].default" so the answer is: Alternative 4: dumb
Bert. Rap knuckles with ruler.

Actually, indexing by a logical matrix doesn't make much  sense to me
in either case, as it does not have the effect of selecting individual
elements, which is what numeric matrix indices do. But that's a matter
of usage, neither bug nor feature.

If I had gotten something like the error message: "Matrix indices not
allowed for replacement in data frames," I would not have been
surprised. But as you said, the behavior **IS** documented.

Best,
Bert



On Tue, May 1, 2012 at 10:49 AM, Ista Zahn <istazahn at gmail.com> wrote:
> Hi Bert,
>
> The failure itself is the documented behavior: ?'[.data.frame' says
>
> "Matrix indexing ('x[i]' with a logical or a 2-column integer
>     matrix 'i') using '[' is not recommended, and barely supported.
>     For extraction, 'x' is first coerced to a matrix.  For
>     replacement, a logical matrix (only) can be used to select the
>     elements to be replaced in the same way as for a matrix."
>
> The error message may be a bit hinky, as obviously data.frames can be
> indexed by things other than logical matricies. Or is there another
> reason this strikes you as odd?
>
> Best,
> Ista
>
> On Tue, May 1, 2012 at 1:33 PM, Bert Gunter <gunter.berton at gene.com> wrote:
>> AdvisoRs:
>>
>> Is the following a bug, feature, hinky error message, or dumb Bert?
>>
>>> mtest <- matrix(1:12,nr=4)
>>> dftest <- data.frame(mtest)
>>> ix <- cbind(1:2,2:3)
>>> mtest[ix] <- NA
>>> mtest
>>     [,1] [,2] [,3]
>> [1,]    1   NA    9
>> [2,]    2    6   NA
>> [3,]    3    7   11
>> [4,]    4    8   12
>>
>> ## But ...
>>> dftest[ix] <- NA
>> Error in `[<-.data.frame`(`*tmp*`, ix, value = NA) :
>>  only logical matrix subscripts are allowed in replacement
>>
>> Obviously, I was expecting matrix indexing for replacement to work
>> similarly in both cases; however, I can see why it would be
>> problematic for data frames (mixed types), but was a bit nonplussed by
>> the error message, which seems hinky to me.
>>
>> Cheers,
>> Bert
>>
>> --
>>
>> Bert Gunter
>> Genentech Nonclinical Biostatistics
>>
>> Internal Contact Info:
>> Phone: 467-7374
>> Website:
>> http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm
>>
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-- 

Bert Gunter
Genentech Nonclinical Biostatistics

Internal Contact Info:
Phone: 467-7374
Website:
http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm