prepend: fails for empty list #637
Description
purrr::prepend fails for empty list due to the checking of the before param though (partly based on the documentation) I would expect it to work as base::append by default. Is there a reason for this?
If you agree that it should work for empty lists as well I am happy to submit a PR.
purrr::prepend(list(), "a")
#> Error in purrr::prepend(list(), "a"): before > 0 && before <= n is not TRUE
append("a", list())
#> [[1]]
#> [1] "a"
purrr::prepend(list("b"), "a")
#> [[1]]
#> [1] "a"
#>
#> [[2]]
#> [1] "b"
append("a", list("b"))
#> [[1]]
#> [1] "a"
#>
#> [[2]]
#> [1] "b"Created on 2019-02-10 by the reprex package (v0.2.0).
My first idea for implementation:
function (x, values, before = 1)
{
n <- length(x)
stopifnot(n == 0 || (before > 0 && before <= n))
if (before == 1) {
c(values, x)
}
else {
c(x[1:(before - 1)], values, x[before:n])
}
}