Sigh. I don't agree with this "avoid ifelse because you might not know the shape of the arguments" advice. All R variables have shapes and sizes, and the better advice is to _pay attention to shapes and sizes_, especially when using vectorized functions like ifelse. An easy way to maintain shape/size consistency is to work with data frames at the top level of your code.
Which is not to say that I use ifelse liberally... it is not the most efficient way to get an answer in many cases. findInterval and cut are often better choices, as is in-place modification: x <- rep( 2, length( a ) ) x[ a < 3 ] <- 1 which can be extended if needed. On July 10, 2019 6:45:55 AM PDT, 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. -- Sent from my phone. Please excuse my brevity. ______________________________________________ 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.
