ROBUSTNESS: x || y and x && y to give warning/error if length(x) != 1 or length(y) != 1
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. 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.bengtsson at 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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