I think this is an excellent idea as it eliminates a situation which is almost certainly user error. Making it an error would break a small amount of existing code (even if for the better), so perhaps it should start as a warning, but be optionally upgraded to an error. It would be nice to have a fixed date (R version) in the future when the default will change to error.
In an ideal world, I think the following four cases should all return the same error: if (logical()) 1 #> Error in if (logical()) 1: argument is of length zero if (c(TRUE, TRUE)) 1 #> Warning in if (c(TRUE, TRUE)) 1: the condition has length > 1 and only the #> first element will be used #> [1] 1 logical() || TRUE #> [1] TRUE c(TRUE, TRUE) || TRUE #> [1] TRUE i.e. I think that `if`, `&&`, and `||` should all check that their input is a logical (or numeric) vector of length 1. Hadley On Tue, Aug 28, 2018 at 10:03 PM 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 > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel -- http://hadley.nz ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
