From wdunl@p @ending from tibco@com  Wed Nov 28 21:10:26 2018
From: wdunl@p @ending from tibco@com (William Dunlap)
Date: Wed, 28 Nov 2018 12:10:26 -0800
Subject: [Rd] named arguments discouraged in `[.data.frame` and
 `[<-.data.frame`
In-Reply-To: <fa0ff7bd9b544890be2ba300d5045473@it-ex11.win.ntnu.no>
References: <fa0ff7bd9b544890be2ba300d5045473@it-ex11.win.ntnu.no>
Message-ID: <CAF8bMcZhZJNbY7MYA=e9AQVCkR9v516b1z6-o9bgKOhq_Z9S1w@mail.gmail.com>

They can get bitten in the last two lines of this example, where the 'x'
argument is not first:
> d <- data.frame(C1=c(r1=11,r2=21,r3=31), C2=c(12,22,32))
> d[1,1:2]
   C1 C2
r1 11 12
> `[`(d,j=1:2,i=1)
   C1 C2
r1 11 12
Warning message:
In `[.data.frame`(d, j = 1:2, i = 1) :
  named arguments other than 'drop' are discouraged
> `[`(j=1:2,d,i=1)
Error in (1:2)[d, i = 1] : incorrect number of dimensions
> do.call("[", list(j=1:2, i=1, x=d))
Error in 1:2[i = 1, x = list(C1 = c(11, 21, 31), C2 = c(12, 22, 32))] :
  incorrect number of dimensions

Bill Dunlap
TIBCO Software
wdunlap tibco.com


On Wed, Nov 28, 2018 at 11:30 AM Henrik P?rn <henrik.parn at 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 at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>

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[Rd] named arguments discouraged in `[.data.frame` and `[<-.data.frame`
William Dunlap