label_every_nth: export this, if scales don't want to

[davidhodge931]

Otherwise, leave it internal

ggplot2 issue raised

[davidhodge931]

#' Hold every nth element
#'
#' @description
#' Hold every nth element in a vector, and replace the rest with "".
#'
#' @param n The increment of elements to hold as is. Defaults to `2`.
#' @param offset An offset for which element to first hold. Defaults to `0`. Possible values are `-1` to (`n - 2`)
#' @param ... If numeric, arguments passed to the `scales::comma` function. Otherwise, arguments passed to `format`.
#'
#' @return A labelling function
#' @noRd
#'
#' @examples
#'  label_every_nth()(scales::comma(seq(1000, 5000, 1000)))
#'  label_every_nth()(lubridate::ymd(c("2021-01-01", "2022-01-01", "2023-01-01", "2024-01-01")))
#'  label_every_nth()(LETTERS[1:12])
#'
#'  library(dplyr)
#'  library(palmerpenguins)
#'
#'  set_blanket()
#'
#'  penguins |>
#'    mutate(across(sex, \(x) stringr::str_to_sentence(x))) |>
#'    gg_point(
#'      x = flipper_length_mm,
#'      y = body_mass_g,
#'      col = sex,
#'      x_labels = label_every_nth(),
#'      y_labels = label_every_nth(),
#'    )
#
label_every_nth <- function(n = 2, offset = 0, ...) {
  function(x) {
    i <- which(is.finite(x) | is.character(x) | is.factor(x) | is.logical(x))
    i <- i[seq_along(i) %% n == (offset + 1)]

    if (is.numeric(x)) x <- scales::comma(x, ...)
    else x <- format(x, ...)

    x[-i] <- ""
    x
  }
}