[R] explicit coercion warnings as.numeric Versus as.logical

[Jim Lemon]

Hi Ramnik,
Bert's answer is correct, and an easy way to see why is to look at:

c(1,F,"b")
[1] "1"     "FALSE" "b"

The reason that "F" is translated to "FALSE" is that is its default
value when R is started. If you change that value:

F<-"foo"
c(1,F,"b")
[1] "1"   "foo" "b"
as.logical(c(1,F,"b"))
[1] NA NA NA

To find out why as.numeric warns you and as.logical doesn't, we will
have to await the response of someone who knows. I suspect that
as.numeric employs a fairly sophisticated analysis of a string to see
if it is a number while as.logical just shoves the value (x) into a
conditional like:

x != 0

Jim


On Tue, Nov 22, 2016 at 2:57 AM, Bert Gunter <bgunter.4567 at gmail.com> wrote:
> Not an answer, but note that your vectors are all first (silently)
> coerced to character, as vectors must be all of one type.
>
> I would hazard a guess that the answer is: it's simply an arbitrary
> inconsistency (different folks wrote the functions at different
> times). Note that AFAICS, the difference has no effect on the behavior
> of the two functions, i.e. the behavior is consistent, which is what
> counts. However, I of course defer to real experts.
>
> -- Bert
> Bert Gunter
>
> "The trouble with having an open mind is that people keep coming along
> and sticking things into it."
> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
>
>
> On Mon, Nov 21, 2016 at 1:52 AM, Ramnik Bansal <ramnik.bansal at gmail.com> wrote:
>> Hi,
>>
>> I am trying to understand under which specific conditions does explicit
>> coercion produce warnings.
>>
>>> as.numeric(c(1, F, "b"))
>> [1]  1 NA NA
>> Warning message:
>> NAs introduced by coercion
>>
>>> as.logical(c(1, F, "b"))
>> [1]    NA FALSE    NA
>>
>>
>> In above examples, as.numeric produces warning but as.logical does not.
>> What is the reason behind this different behaviour. Ideally as.logical
>> should also have produced the warning message like as.numeric.
>>
>> Thanks in advance.
>> Ramnik
>>
>>         [[alternative HTML version deleted]]
>>
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> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.