On 08/30/2018 01:56 PM, Joris Meys wrote:
I have to agree with Emil here. && and || are short circuited like in C and
C++. That means that
TRUE || c(TRUE, FALSE)
FALSE && c(TRUE, FALSE)
cannot give an error because the second part is never evaluated. Throwing a
warning or error for
c(TRUE, FALSE) || TRUE
would mean that the operator gives a different result depending on the
order of the objects, breaking the symmetry. Also that would be undesirable.
Note that `||` and `&&` have never been symmetric:
TRUE || stop() # returns TRUE
stop() || TRUE # returns an error
Regarding logical(0): per the documentation, it is indeed so that ||, &&
and isTRUE always return a length-one logical vector. Hence the NA.
On a sidenote: there is no such thing as a scalar in R. What you call
scalar, is really a length-one vector. That seems like a detail, but is
important in understanding why this admittedly confusing behaviour actually
makes sense within the framework of R imho. I do understand your objections
and suggestions, but it would boil down to removing short circuited
operators from R.
My 2 cents.
Cheers
Joris
On Wed, Aug 29, 2018 at 5:03 AM Henrik Bengtsson <henrik.bengts...@gmail.com>
wrote:
# Issue
'x || y' performs 'x[1] || y' for length(x) > 1. For instance (here
using R 3.5.1),
c(TRUE, TRUE) || FALSE
[1] TRUE
c(TRUE, FALSE) || FALSE
[1] TRUE
c(TRUE, NA) || FALSE
[1] TRUE
c(FALSE, TRUE) || FALSE
[1] FALSE
This property is symmetric in LHS and RHS (i.e. 'y || x' behaves the
same) and it also applies to 'x && y'.
Note also how the above truncation of 'x' is completely silent -
there's neither an error nor a warning being produced.
# Discussion/Suggestion
Using 'x || y' and 'x && y' with a non-scalar 'x' or 'y' is likely a
mistake. Either the code is written assuming 'x' and 'y' are scalars,
or there is a coding error and vectorized versions 'x | y' and 'x & y'
were intended. Should 'x || y' always be considered an mistake if
'length(x) != 1' or 'length(y) != 1'? If so, should it be a warning
or an error? For instance,
'''r
x <- c(TRUE, TRUE)
y <- FALSE
x || y
Error in x || y : applying scalar operator || to non-scalar elements
Execution halted
What about the case where 'length(x) == 0' or 'length(y) == 0'? Today
'x || y' returns 'NA' in such cases, e.g.
logical(0) || c(FALSE, NA)
[1] NA
logical(0) || logical(0)
[1] NA
logical(0) && logical(0)
[1] NA
I don't know the background for this behavior, but I'm sure there is
an argument behind that one. Maybe it's simply that '||' and '&&'
should always return a scalar logical and neither TRUE nor FALSE can
be returned.
/Henrik
PS. This is in the same vein as
https://mailman.stat.ethz.ch/pipermail/r-devel/2017-March/073817.html
- in R (>=3.4.0) we now get that if (1:2 == 1) ... is an error if
_R_CHECK_LENGTH_1_CONDITION_=true
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