The answer here is that in "ifelse(a < 3, ......)" you ALWAYS expect "a" to be a vector because there would be no point in using ifelse if it weren't. If you believe that "a" is or ought to be a single number, you write x <- if (a < 3) 1 else 2 The whole point of ifelse is to vectorise.
On Thu, 11 Jul 2019 at 01:47, Eric Berger <ericjber...@gmail.com> wrote: > Or even > > a <- 1:5 > > [lots of other code] > > x <- ifelse( a < 3, 1, 2) > > The point (in this example) is that you might have introduced a bug because > you forgot that 'a' is a vector. > Looking (in isolation) at the assignment to 'x' you believe it's going to > be a single number, either 1 or 2 (unless you know the "shape" of a). > I've been burned by such issues. > > > On Wed, Jul 10, 2019 at 4:42 PM Eric Berger <ericjber...@gmail.com> wrote: > > > For example, can you predict what the following code will do? > > > a <- 1:5 > > > b <- c(2,3) > > > ifelse( a < 3, 1, b) > > > > > > On Wed, Jul 10, 2019 at 4:34 PM José María Mateos <ch...@rinzewind.org> > > wrote: > > > >> On Wed, Jul 10, 2019, at 04:39, Eric Berger wrote: > >> > 1. The ifelse() command is a bit tricky in R. Avoiding it is often a > >> good > >> > policy. > >> > >> You piqued my curiosity, can you elaborate a bit more on this? > >> > >> -- > >> José María (Chema) Mateos || https://rinzewind.org > >> > >> ______________________________________________ > >> 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. > >> > > > > [[alternative HTML version deleted]] > > ______________________________________________ > 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. > [[alternative HTML version deleted]] ______________________________________________ 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.
