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.ban...@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.
Duncan Murdoch
______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
