[R] [FORGED] Logical Operators' inconsistent Behavior

[Duncan Murdoch]

On 20/05/2017 5:53 AM, Martin Maechler wrote:
>>>>>> Ramnik Bansal <ramnik.bansal at gmail.com>
>>>>>>     on Sat, 20 May 2017 08:52:55 +0530 writes:
>
>     > Taking this question further.
>     > If I use a complex number or a numeric as an operand in logical
>     > operations, to me it APPEARS that these two types are first coerced to
>     > LOGICAL internally and then THIS logical output is further used as the
>     > operand.
>
>     > For eg.
>     >> x <- 4+5i; c(x & F, x & T, x | F, x | T)
>     > [1] FALSE  TRUE  TRUE  TRUE
>
>     > This output is consistent with
>     >> x <- 4+5i; c(as.logical(x) & F, as.logical(x) & T, as.logical(x) | F, as.logical(x) | T)
>     > [1] FALSE  TRUE  TRUE  TRUE
>
>     > This consistency makes me draw an on-the-surface conclusion that in
>     > the case of logical operations if the operand is not of type 'logical'
>     > it is first coerced into 'logical'.
>
> That conclusion is wrong as you show below.
> Rather, as the error message says,
> logical
> 	"operations are possible only for numeric, logical or complex types"
>
> Again:
>
> 1) Logical/Arithmetic  operations "work" with "numeric-like" types, namely
>   numeric, logical or complex, (and numeric = {integer, double})
>
>   ==> all other types give an error (the one you've cited twice)
>
> 2) For "numeric-like" types and *logical* operations (&, |, !; plus && and ||)
>    the equivalent of as.logical() is applied before performing the Op.
>
> Seems pretty consistent ...
> and also according to the principle of "least surprise" (for me at least).
>

The surprise is that as.logical("TRUE") returns TRUE, whereas automatic 
coercion doesn't apply to character strings.  I don't think we should 
change this, but it is an inconsistency.  (We could perhaps mention it 
in the ?logical help page.)

Duncan Murdoch

Duncan Murdoch