[Rd] ROBUSTNESS: x || y and x && y to give warning/error if length(x) != 1 or length(y) != 1
Dénes Tóth
toth@dene@ @ending from kogentum@hu
Thu Aug 30 14:09:51 CEST 2018
On 08/30/2018 01:56 PM, Joris Meys wrote:
> I have to agree with Emil here. && and || are short circuited like in C and
> C++. That means that
>
> TRUE || c(TRUE, FALSE)
> FALSE && c(TRUE, FALSE)
>
> cannot give an error because the second part is never evaluated. Throwing a
> warning or error for
>
> c(TRUE, FALSE) || TRUE
>
> would mean that the operator gives a different result depending on the
> order of the objects, breaking the symmetry. Also that would be undesirable.
Note that `||` and `&&` have never been symmetric:
TRUE || stop() # returns TRUE
stop() || TRUE # returns an error
>
> Regarding logical(0): per the documentation, it is indeed so that ||, &&
> and isTRUE always return a length-one logical vector. Hence the NA.
>
> On a sidenote: there is no such thing as a scalar in R. What you call
> scalar, is really a length-one vector. That seems like a detail, but is
> important in understanding why this admittedly confusing behaviour actually
> makes sense within the framework of R imho. I do understand your objections
> and suggestions, but it would boil down to removing short circuited
> operators from R.
>
> My 2 cents.
> Cheers
> Joris
>
> On Wed, Aug 29, 2018 at 5:03 AM Henrik Bengtsson <henrik.bengtsson using gmail.com>
> wrote:
>
>> # Issue
>>
>> 'x || y' performs 'x[1] || y' for length(x) > 1. For instance (here
>> using R 3.5.1),
>>
>>> c(TRUE, TRUE) || FALSE
>> [1] TRUE
>>> c(TRUE, FALSE) || FALSE
>> [1] TRUE
>>> c(TRUE, NA) || FALSE
>> [1] TRUE
>>> c(FALSE, TRUE) || FALSE
>> [1] FALSE
>>
>> This property is symmetric in LHS and RHS (i.e. 'y || x' behaves the
>> same) and it also applies to 'x && y'.
>>
>> Note also how the above truncation of 'x' is completely silent -
>> there's neither an error nor a warning being produced.
>>
>>
>> # Discussion/Suggestion
>>
>> Using 'x || y' and 'x && y' with a non-scalar 'x' or 'y' is likely a
>> mistake. Either the code is written assuming 'x' and 'y' are scalars,
>> or there is a coding error and vectorized versions 'x | y' and 'x & y'
>> were intended. Should 'x || y' always be considered an mistake if
>> 'length(x) != 1' or 'length(y) != 1'? If so, should it be a warning
>> or an error? For instance,
>> '''r
>>> x <- c(TRUE, TRUE)
>>> y <- FALSE
>>> x || y
>>
>> Error in x || y : applying scalar operator || to non-scalar elements
>> Execution halted
>>
>> What about the case where 'length(x) == 0' or 'length(y) == 0'? Today
>> 'x || y' returns 'NA' in such cases, e.g.
>>
>>> logical(0) || c(FALSE, NA)
>> [1] NA
>>> logical(0) || logical(0)
>> [1] NA
>>> logical(0) && logical(0)
>> [1] NA
>>
>> I don't know the background for this behavior, but I'm sure there is
>> an argument behind that one. Maybe it's simply that '||' and '&&'
>> should always return a scalar logical and neither TRUE nor FALSE can
>> be returned.
>>
>> /Henrik
>>
>> PS. This is in the same vein as
>> https://mailman.stat.ethz.ch/pipermail/r-devel/2017-March/073817.html
>> - in R (>=3.4.0) we now get that if (1:2 == 1) ... is an error if
>> _R_CHECK_LENGTH_1_CONDITION_=true
>>
>> ______________________________________________
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>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>
>
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