R/ptd_rebase.R

In NHSRplotthedots: Draw XmR Charts for NHSE/I 'Making Data Count' Programme

#' Rebase
#'
#' Produces an object that can be used for rebasing an SPC chart. This method provides two different ways to rebase:
#'   1. You can either provide a single vector of dates, which will rebase every facet of an SPC with the same dates
#'   2. You can provide named vectors of dates, where the names correspond to the names of the facets, in order to
#'      rebase a facetted chart
#'
#' @param ... either a single vector of dates, or, named vectors of dates. See examples.
#'
#' @return a list
#'
#' @export
#'
#' @examples
#' # if you aren't using a facetted chart, or you want to rebase each facet at the same dates, then
#' # you can simply call this method with a vector of dates. For example, to rebase on the 1^st^
#' # January 2020 and 22^nd^ March 2020:
#'
#' ptd_rebase(as.Date(c("2020-01-01", "2020-03-22")))
#'
#' # if you are using a facetted chart, and wish to rebase each facet with different dates, then
#' # you can call this method, naming each vector of dates with the name of the facet. If there are
#' # facet's that you don't need to rebase you can simply ignore them. For example, if you had a
#' # chart with facets "a", "b", and "c", and you wanted to rebase "a" on the 1^st^ January 2020,
#' # and "b" on the 22^nd^ March 2020:
#'
#' ptd_rebase(
#'   "a" = as.Date("2020-01-01"),
#'   "b" = as.Date("2020-03-22")
#' )
ptd_rebase <- function(...) {
  rebase <- list(...)

  if (length(rebase) == 0) {
    return(NULL)
  }

  if (length(rebase) == 1 && is.null(names(rebase))) {
    assertthat::assert_that(
      is_date(rebase[[1]]),
      msg = "ptd_rebase(): all items must be date vectors."
    )
    return(rebase[[1]])
  }

  assertthat::assert_that(
    !is.null(names(rebase)),
    all(names(rebase) != ""),
    msg = "ptd_rebase(): some items are not named."
  )

  assertthat::assert_that(
    all(vapply(rebase, is_date, logical(1))),
    msg = "ptd_rebase(): all items must be date vectors."
  )

  rebase
}