Whenever they are calling a primitive, because primitives match arguments positionally. Of course, you then you need to introduce the concept of a primitive.
You could also make an argument from the code clarity perspective, as typically primitives have simple interfaces and/or are used frequently enough that naming arguments just introduces clutter. That probably requires experience though. Michael On Wed, Nov 28, 2018 at 11:30 AM Henrik Pärn <henrik.p...@ntnu.no> wrote: > > tl;dr: > > Why are named arguments discouraged in `[.data.frame`, `[<-.data.frame` and > `[[.data.frame`? > > (because this question is of the kind 'why is R designed like this?', I > though R-devel would be more appropriate than R-help) > > ############################# > > Background: > > Now and then students presents there fancy functions like this: > > myfancyfun(d,12,0.3,0.2,500,1000,FALSE,TRUE,FALSE,TRUE,FALSE) > > Incomprehensible. Thus, I encourage them to use spaces and name arguments, > _at least_ when trying to communicate their code with others. Something like: > > myfancyfun(data = d, n = 12, gamma = 0.3, prob = 0.2, > size = 500, niter = 1000, model = FALSE, > scale = TRUE, drop = FALSE, plot = TRUE, save = FALSE) > > > Then some overzealous students started to use named arguments everywhere. > E-v-e-r-y-w-h-e-r-e. Even in the most basic situation when indexing vectors > (as a subtle protest?), like: > > vec <- 1:9 > > vec[i = 4] > `[`(x = vec, i = 4) > > vec[[i = 4]] > `[[`(x = vec, i = 4) > > vec[i = 4] <- 10 > `[<-`(x = vec, i = 4, value = 10) > > ...or when indexing matrices: > > m <- matrix(vec, ncol = 3) > m[i = 2, j = 2] > `[`(x = m, i = 2, j = 2) > # 5 > > m[i = 2, j = 2] <- 0 > `[<-`(x = m, i = 2, j = 2, value = 0) > > ###### > > This practice indeed feels like overkill, but it didn't seem to hurt either. > Until they used it on data frames. Then suddenly warnings appeared that named > arguments are discouraged: > > d <- data.frame(m) > > d[[i = "X2"]] > # [1] 4 5 6 > # Warning message: > # In `[[.data.frame`(d, i = "X2") : > # named arguments other than 'exact' are discouraged > > d[i = 2, j = 2] > # [1] 0 > # Warning message: > # In `[.data.frame`(d, i = 2, j = 2) : > # named arguments other than 'drop' are discouraged > > d[i = 2, j = 2] <- 5 > # Warning message: > # In `[<-.data.frame`(`*tmp*`, i = 2, j = 2, value = 5) : > # named arguments are discouraged > > > ################################## > > Of course I could tell them "don't do it, it's overkill and not common > practice" or "it's just a warning, don't worry". However, I assume the > warnings are there for a good reason. > > So how do I explain to the students that named arguments are actively > discouraged in `[.data.frame` and `[<-.data.frame`, but not in `[` and `[<-`? > When will they get bitten? > > ______________________________________________ > 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
