intersect() is a generic function so the question is which one does someone want to know if it remains in the same order?
But a deeper question is what ORDER? intersect(A, B) intersect(B, A) Note the results have to be the same but not the order unless they start sorted the same way. -----Original Message----- From: R-help <r-help-boun...@r-project.org> On Behalf Of Duncan Murdoch Sent: Sunday, October 17, 2021 5:49 AM To: petr smirnov <psmirnov2...@gmail.com>; r-help@r-project.org Subject: Re: [R] Does intersect preserve order? On 15/10/2021 4:31 p.m., petr smirnov wrote: > Hi, > > Is base::intersect guaranteed to return items in the order they > (first) appear in the first argument? I couldn't find any mention of > this in the help file for set operations. No, that's just what the current implementation does. It's conceivable that swapping x and y could let it be faster in some circumstances. Or maybe there's a completely different implementation that's better for some data types. In either of those cases the order could change. Generally speaking, the functions that treat vectors as sets make no assumptions and no guarantees about order, because sets are unordered. If you need the current behaviour to be guaranteed, probably the easiest way is to copy the function: it's very simple. Duncan Murdoch > > If so, could this be documented on the help page? > > Thanks, > Petr ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
