[R] [FORGED] Re: [FORGED] Logical Operators' inconsistent Behavior

[Ramnik Bansal]

In the case of logical operations performed with an operand being a
character type, the error is:
"operations are possible only for numeric, logical or complex types"

Now the display of this error message seems to be the OUTCOME of the
fact that implicit coercion is NOT BEING APPLIED INTERNALLY to
character operands in the case of logical operations but is applied to
all other "numeric" type operands. This error message is NOT the
CAUSE.

Well, why not:

F & "abc" return a FALSE because if F & NA can return  FALSE, the
logic being that once an operand is FALSE in case of AND operation
then the output should be False, IRRESPECTIVE of the second operand.
In that case how does it matter if the second operand  is "abc" or
4+5i or NA? The output is deterministically FALSE anyways.

Effectively the point that I want to make is: Treat the character
operand as NA ( except "F", "FALSE", "T", "TRUE" etc which can be
treated as FALSE/TRUE) and then apply the logical operations. Or in
short "Apply implicit coercion on character types as well in case of
logical operations."




On Sat, May 20, 2017 at 4:15 PM, Rolf Turner <r.turner at auckland.ac.nz> wrote:
> On 20/05/17 22:42, Duncan Murdoch wrote:
>>
>> On 20/05/2017 6:39 AM, Rolf Turner wrote:
>>>
>>> On 20/05/17 22:18, Duncan Murdoch wrote:
>>>>
>>>> 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.)
>>>
>>>
>>>
>>> Actually it *is* mentioned.  From ?logical:
>>>
>>>> Character strings c("T", "TRUE", "True", "true") are regarded as
>>>> true,  c("F", "FALSE", "False", "false") as false, and all others as NA.
>>>
>>>
>>
>> I meant that the negative part should be mentioned:  this only works
>> with an explicit as.logical(), not with implicit coercion.
>
>
> Ah, I see.  I missed the point.
>
>
> cheers,
>
> Rolf
>
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