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rep(): Expecting an argument-is-missing error, but ...

4 messages · Henrik Bengtsson, Rui Barradas, Peter Langfelder +1 more

Original
Henrik Bengtsson
# 
What's going on here:

$ R --vanilla --quiet
[1] "x"

?
[1] ?4.5.2?

/Henrik
Rui Barradas
# 
?s 06:40 de 11/12/2025, Henrik Bengtsson escreveu:
Hello,

I can reproduce this on Windows.


Microsoft Windows [Version 10.0.22631.5039]
(c) Microsoft Corporation. Todos os direitos reservados.

C:\>R --vanilla --quiet
 > f <- function(n) rep("x", times = n)
 > f
function(n) rep("x", times = n)
 > f()
[1] "x"
 > getRversion()
[1] '4.5.2'
 > g <- function(n) rep(1, times = n)
 > g
function(n) rep(1, times = n)
 > g()
[1] 1
 > h <- function(n) rep(1, n)
 > h
function(n) rep(1, n)
 > h()
[1] 1
 > i <- function(n) rep(1, each = n)
 > i()
[1] 1
 > sessionInfo()
R version 4.5.2 (2025-10-31 ucrt)
Platform: x86_64-w64-mingw32/x64
Running under: Windows 11 x64 (build 22631)

Matrix products: default
   LAPACK version 3.12.1

locale:
[1] LC_COLLATE=Portuguese_Portugal.utf8  LC_CTYPE=Portuguese_Portugal.utf8
[3] LC_MONETARY=Portuguese_Portugal.utf8 LC_NUMERIC=C
[5] LC_TIME=Portuguese_Portugal.utf8

time zone: Europe/Lisbon
tzcode source: internal

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

loaded via a namespace (and not attached):
[1] compiler_4.5.2 tools_4.5.2
 > q()


Hope this helps,

Rui Barradas
Peter Langfelder
# 
I think it's a bit of a quirk of rep:
Help of 'rep' does state this:

The default behaviour is as if the call was

       rep(x, times = 1, length.out = NA, each = 1)

So it seems to even be documented.

Peter


Peter

On Thu, Dec 11, 2025 at 2:40?PM Henrik Bengtsson
<henrik.bengtsson at gmail.com> wrote:
Serguei Sokol
# 
Le 11/12/2025 ? 09:21, Peter Langfelder a ?crit?:
Right. But I think the initial question was rather "why f() does not 
complain about missing n?"
It is because 'n' is not used in f() itself, it's just passed through in 
his quality of "missing".

If you define f() where 'n' is used in some way, e.g. as follows:

f=function(n) rep("x", times=n+0L)

then it complains:

f()
Error in f() (from #1) : argument "n" is missing, with no default

Serguei.