R/helpers.R

In BWAM/validator: What the Package Does (One Line, Title Case)

#' Get a List Element
#'
#' @param .list a named list object.
#' @param .pattern a regular expression to be matched to a character string.
#'
#' @return a single element of a list.
#'
#' @examples
#' get_element(.list = list(first_element = 1:3, second_element = 4:6), .pattern = "second")

get_element <- function(.list, .pattern) {
  # A named list is required
  if (is.null(names(.list))) stop(".list must contain named elements.")
  # Identify the list names that match the provided pattern
  pattern_vec <- grepl(pattern = .pattern,
                       x = names(.list),
                       perl = TRUE)
  # Identify the matched names
  name_vec <- names(.list)[pattern_vec]
  # Ensure that only one name was matched
  if (length(name_vec) != 1) {
    stop(
      "Matched list names must be length 1. \n",
      "\t Pattern:", .pattern, "\n",
      "\t Matches:", paste(name_vec, collapse = ", \n\t\t")
    )
  }
  # Extract the element from the list
  .list[[name_vec]]
}