I have to disagree, I think one of the advantages of '||' (or &&) is the lazy evaluation, i.e. you can use the first condition to "not care" about the second (and stop errors from being thrown). So if I want to check if x is a length-one numeric with value a value between 0 and 1, I can do 'class(x)=='numeric' && length(x)==1 && x>0 && x<1'. In your proposal, having x=c(1,2) would throw an error or multiple warnings. Also code that relies on the second argument not being evaluated would break, as we need to evaluate y in order to know length(y) There may be some benefit in checking for length(x) only, though that could also cause some false positives (e.g. 'x==-1 || length(x)==0' would be a bit ugly, but not necessarily wrong, same for someone too lazy to write x[1] instead of x).
And I don’t really see the advantage. The casting to length one is (I think), a feature, not a bug. If I have/need a length one x, and a length one y, why not use '|' and '&'? I have to admit I only use them in if-statements, and if I need an error to be thrown when x and y are not length one, I can use the shorter versions and then the if throws a warning (or an error for a length-0 or NA result). I get it that for someone just starting in R, the differences between | and || can be confusing, but I guess that's just the price to pay for having a vectorized language. Best regards, Emil Bode Data-analyst +31 6 43 83 89 33 emil.b...@dans.knaw.nl DANS: Netherlands Institute for Permanent Access to Digital Research Resources Anna van Saksenlaan 51 | 2593 HW Den Haag | +31 70 349 44 50 | i...@dans.knaw.nl <mailto:i...@dans.kn> | dans.knaw.nl <applewebdata://71F677F0-6872-45F3-A6C4-4972BF87185B/www.dans.knaw.nl> DANS is an institute of the Dutch Academy KNAW <http://knaw.nl/nl> and funding organisation NWO <http://www.nwo.nl/>. On 29/08/2018, 05:03, "R-devel on behalf of Henrik Bengtsson" <r-devel-boun...@r-project.org on behalf of 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 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
