R devel - Jan 2026 - rep.int and rep_len do not drop names attribute

Hello,

In the documentation for ?rep, sections Value and Note say that


 > Value
 > An object of the same type as x.

 > rep.int and rep_len return no attributes (except the class if 
returning a factor).

 > The default method of rep gives the result names (which will almost 
always contain duplicates) if x had names, but retains no other 
attributes.


 > Note
 > Function rep.int is a simple case which was provided as a separate 
function partly for S compatibility and partly for speed (especially 
when names can be dropped). The performance of rep has been improved 
since, but rep.int is still at least twice as fast when x has names.


And this works as documented.


y <- 1:4
names(y) <- letters[1:4]
class(y) <- "new_class"
attr(y, "this") <- "that"

y
#> a b c d
#> 1 2 3 4
#> attr(,"class")
#> [1] "new_class"
#> attr(,"this")
#> [1] "that"

rep(y, 2)      # keeps names only
#> a b c d a b c d
#> 1 2 3 4 1 2 3 4

rep.int(y, 2)  # no names and no other attributes
#> [1] 1 2 3 4 1 2 3 4

rep_len(y, 2)  # no names and no other attributes
#> [1] 1 2



But in the documentation's last example, the factor example, the names 
attribute is not dropped.



## named factor
x <- factor(LETTERS[1:4]); names(x) <- letters[1:4]
x
#> a b c d
#> A B C D
#> Levels: A B C D

rep(x, 2)
#> a b c d a b c d
#> A B C D A B C D
#> Levels: A B C D

rep(x, each = 2)
#> a a b b c c d d
#> A A B B C C D D
#> Levels: A B C D

rep.int(x, 2)  # no names  <--- Wrong comment
#> a b c d a b c d
#> A B C D A B C D
#> Levels: A B C D

rep_len(x, 10)
#> a b c d a b c d a b
#> A B C D A B C D A B
#> Levels: A B C D



Further test with attributes()



rep.int(x, 2) |> attributes()
#> $names
#> [1] "a" "b" "c" "d" "a"
"b" "c" "d"
#>
#> $class
#> [1] "factor"
#>
#> $levels
#> [1] "A" "B" "C" "D"

rep_len(x, 10) |> attributes()
#> $names
#>  [1] "a" "b" "c" "d" "a"
"b" "c" "d" "a" "b"
#>
#> $class
#> [1] "factor"
#>
#> $levels
#> [1] "A" "B" "C" "D"



If I'm reading the docs right, this is wrong, isn't it?


Hope this helps,

Rui Barradas

This is a consequence of the following change in R 4.0.0 (r77905):

     ? When internal dispatch for ?rep.int()? and ?rep_len()?
       fails, there is an attempt to dispatch on the equivalent
       call to ?rep()?.

I believe it wasn't intended to change the handling of factors and I 
think it would be desirable to restore the original (and still 
documented) behavior of dropping names for rep.int(<factor>) and 
rep_len(<factor>), so skip the (early) 'rep' fallback if
`inherits(s,
"factor")`.

It would be good to report this in R's Bugzilla 
<https://bugs.R-project.org/>, so there is a PR# for future reference. 
At a first glance the patch looks simple (and should include a 
regression test).

	Sebastian Meyer


Am 25.01.26 um 11:32 schrieb Rui Barradas:
> Hello,
> 
> In the documentation for ?rep, sections Value and Note say that
> 
> 
>  > Value
>  > An object of the same type as x.
> 
>  > rep.int and rep_len return no attributes (except the class if 
> returning a factor).
> 
>  > The default method of rep gives the result names (which will almost 
> always contain duplicates) if x had names, but retains no other attributes.
> 
> 
>  > Note
>  > Function rep.int is a simple case which was provided as a separate 
> function partly for S compatibility and partly for speed (especially 
> when names can be dropped). The performance of rep has been improved 
> since, but rep.int is still at least twice as fast when x has names.
> 
> 
> And this works as documented.
> 
> 
> y <- 1:4
> names(y) <- letters[1:4]
> class(y) <- "new_class"
> attr(y, "this") <- "that"
> 
> y
> #> a b c d
> #> 1 2 3 4
> #> attr(,"class")
> #> [1] "new_class"
> #> attr(,"this")
> #> [1] "that"
> 
> rep(y, 2)????? # keeps names only
> #> a b c d a b c d
> #> 1 2 3 4 1 2 3 4
> 
> rep.int(y, 2)? # no names and no other attributes
> #> [1] 1 2 3 4 1 2 3 4
> 
> rep_len(y, 2)? # no names and no other attributes
> #> [1] 1 2
> 
> 
> 
> But in the documentation's last example, the factor example, the names 
> attribute is not dropped.
> 
> 
> 
> ## named factor
> x <- factor(LETTERS[1:4]); names(x) <- letters[1:4]
> x
> #> a b c d
> #> A B C D
> #> Levels: A B C D
> 
> rep(x, 2)
> #> a b c d a b c d
> #> A B C D A B C D
> #> Levels: A B C D
> 
> rep(x, each = 2)
> #> a a b b c c d d
> #> A A B B C C D D
> #> Levels: A B C D
> 
> rep.int(x, 2)? # no names? <--- Wrong comment
> #> a b c d a b c d
> #> A B C D A B C D
> #> Levels: A B C D
> 
> rep_len(x, 10)
> #> a b c d a b c d a b
> #> A B C D A B C D A B
> #> Levels: A B C D
> 
> 
> 
> Further test with attributes()
> 
> 
> 
> rep.int(x, 2) |> attributes()
> #> $names
> #> [1] "a" "b" "c" "d"
"a" "b" "c" "d"
> #>
> #> $class
> #> [1] "factor"
> #>
> #> $levels
> #> [1] "A" "B" "C" "D"
> 
> rep_len(x, 10) |> attributes()
> #> $names
> #>? [1] "a" "b" "c" "d"
"a" "b" "c" "d" "a"
"b"
> #>
> #> $class
> #> [1] "factor"
> #>
> #> $levels
> #> [1] "A" "B" "C" "D"
> 
> 
> 
> If I'm reading the docs right, this is wrong, isn't it?
> 
> 
> Hope this helps,
> 
> Rui Barradas
> 
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