[R] [FORGED] Logical Operators' inconsistent Behavior

Martin Maechler maechler at stat.math.ethz.ch
Sat May 20 11:53:26 CEST 2017

>>>>> 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)

    > 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)

    > 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,
	"operations are possible only for numeric, logical or complex types"


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).

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