I would add my support for the change. >From a cursory survey of existing code, I'd say that usage like `class(x) == 'y'` -- rather than inherits(x, 'y') or is.y -- is probably going to be the major source of new warnings. So perhaps in the NEWS item it could be noted as a clue for developers encountering nascent warnings.
Of course `if (class(x) == 'y')` already throws a warning, just not `if (class(x) == 'y' && TRUE)`. On Thu, 30 Aug 2018 at 21:09 Emil Bode <[email protected]> wrote: > 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 > [email protected] > > DANS: Netherlands Institute for Permanent Access to Digital Research > Resources > Anna van Saksenlaan 51 | 2593 HW Den Haag > <https://maps.google.com/?q=Anna+van+Saksenlaan+51+%7C+2593+HW+Den+Haag&entry=gmail&source=g> > | +31 70 349 44 50 | [email protected] <mailto:[email protected]> | > 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" < > [email protected] on behalf of [email protected]> > 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 > > ______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > > > ______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > [[alternative HTML version deleted]] ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
