R/match_consecutive_delimiters.R

In rock: Reproducible Open Coding Kit

#' Match the corresponding indices of (YAML) delimiters in a sequential list
#'
#' This is just a convenience function that takes a vector of deliminaters
#' and returns a list of delimiter pairs.
#'
#' @param x The vector with delimiter indices
#' @param errorOnInvalidX Whether to return `NA` (if `FALSE`) or throw an
#' error (if `TRUE`) when `x` is `NULL`, `NA`, or has less than 2 elements.
#' @param errorOnOdd Whether to throw an error if the number of delimiter
#' indices is odd.
#' @param onOddIgnoreFirst If the number of delimiter indices is odd and no
#' error is thrown, whether to ignore the first (`TRUE`) or the last (`FALSE`)
#' delimiter.
#'
#' @return A list where each element is a two-element vector with the two
#' consecutive delimiters
#'
#' @export
#'
#' @examples rock::match_consecutive_delimiters(
#'   c(1, 3, 5, 10, 19, 25, 30, 70)
#' );
#'
#' exampleText <- c(
#'   "some text",
#'   "delimiter",
#'   "more text",
#'   "delimiter",
#'   "filler text",
#'   "intentionally left blank",
#'   "delimiter",
#'   "final text",
#'   "delimiter"
#' );
#'
#' rock::match_consecutive_delimiters(
#'   grep(
#'     "delimiter",
#'     exampleText
#'   )
#' );
match_consecutive_delimiters <- function(x,
                                         errorOnInvalidX = FALSE,
                                         errorOnOdd = FALSE,
                                         onOddIgnoreFirst = FALSE) {
  if (length(x) < 2) {
    if (errorOnInvalidX) {
      stop("The vector with delimiters you passed cannot be matched.");
    } else {
      return(NA);
    }
  }
  ### Check whether we have an odd number of delimiters
  if ((length(x) %% 2) != 0) {
    if (errorOnOdd) {
      stop("An uneven number of delimiters (", length(x), ") was passed!");
    } else if (onOddIgnoreFirst) {
      x <- utils::tail(x, -1);
    } else {
      x <- utils::head(x, -1);
    }
  }
  xIndices <- seq_along(x);
  startIndices <- ((xIndices %% 2) != 0);
  endIndices <- ((xIndices %% 2) == 0);
  return(
    mapply(
      c,
      x[startIndices],
      x[endIndices],
      SIMPLIFY = FALSE
    )
  );
}