Repeat a vector using ALTREP

Creates a repeated vector backed by an ALTREP representation, avoiding materialisation of the full vector in memory until necessary.

Usage

rep_altrep(x, times = 1L, each = 1L)

Arguments

x

A vector to repeat. Must be one of: double, integer, logical, complex, raw, character, or list (including classed variants thereof).

times

A single positive integer giving the number of times to repeat the whole (each-expanded) pattern. Defaults to 1L.

each

A single positive integer giving the number of times each element is repeated before moving to the next. Defaults to 1L.

Value

An ALTREP vector of the same type and class as x, with length length(x) * each * times.

Details

Supported types: double, integer, logical, complex, raw, character, and list. Classed vectors (e.g. factor, Date, POSIXct) are handled transparently: the class attribute is preserved on the returned object so S3 dispatch continues to work without forcing materialisation.

times and each can be combined freely, matching the behaviour of base::rep(): each replicates individual elements first, then times repeats the resulting pattern. Providing only times is equivalent to rep(x, times = times); providing only each is equivalent to rep(x, each = each).

Examples

rep_altrep(letters[1:4], times = 2)
#> [1] "a" "b" "c" "d" "a" "b" "c" "d"
rep_altrep(letters[1:4], each = 2)
#> [1] "a" "a" "b" "b" "c" "c" "d" "d"
rep_altrep(letters[1:4], times = 2, each = 3)
#>  [1] "a" "a" "a" "b" "b" "b" "c" "c" "c" "d" "d" "d" "a" "a" "a" "b" "b" "b" "c"
#> [20] "c" "c" "d" "d" "d"
rep_altrep(1L:4L, each = 2L)
#> [1] 1 1 2 2 3 3 4 4
rep_altrep(c(TRUE, FALSE, NA), each = 2L, times = 3L)
#>  [1]  TRUE  TRUE FALSE FALSE    NA    NA  TRUE  TRUE FALSE FALSE    NA    NA
#> [13]  TRUE  TRUE FALSE FALSE    NA    NA
rep_altrep(factor(c("a", "b", "c")), each = 2L)
#> [1] a a b b c c
#> Levels: a b c
rep_altrep(as.Date("2024-01-01") + 0:2, each = 2L)
#> [1] "2024-01-01" "2024-01-01" "2024-01-02" "2024-01-02" "2024-01-03"
#> [6] "2024-01-03"
rep_altrep(c("foo", "bar"), times = 5L)
#>  [1] "foo" "bar" "foo" "bar" "foo" "bar" "foo" "bar" "foo" "bar"
rep_altrep(list(1, "a", TRUE), each = 2L, times = 2L)
#> [[1]]
#> [1] 1
#> 
#> [[2]]
#> [1] 1
#> 
#> [[3]]
#> [1] "a"
#> 
#> [[4]]
#> [1] "a"
#> 
#> [[5]]
#> [1] TRUE
#> 
#> [[6]]
#> [1] TRUE
#> 
#> [[7]]
#> [1] 1
#> 
#> [[8]]
#> [1] 1
#> 
#> [[9]]
#> [1] "a"
#> 
#> [[10]]
#> [1] "a"
#> 
#> [[11]]
#> [1] TRUE
#> 
#> [[12]]
#> [1] TRUE
#>