R/fold.R

In gpilgrim2670/SwimmeR: Data Import, Cleaning, and Conversions for Swimming Results

#' Fold a vector onto itself
#'
#' @param x a vector
#' @param block.size the size of groups in which to block the data
#' @return a new vector in the following order: first block, last block, second
#'   block, second-to-last block, ...
#'
#' @references from the seemingly now defunct \code{mRchmadness} package by Eli
#'   Shayer and Saber Powers and used per the terms of that package's GPL-2
#'   license

fold <- function(x, block.size = 1) {

  num.blocks <- length(x) / block.size

  # Sanitize inputs
  if (length(x) %% block.size != 0) {
    stop("length(x) / block.size must be an integer.")
  }
  if (num.blocks %% 2 != 0) {
    stop("Number of blocks must be even.")
  }

  # Split by block
  blocks <- split(x, rep(1:num.blocks, each = block.size))

  names(blocks) <- NULL

  # Fold by block
  unlist(blocks[order(c(1:(num.blocks/2), (num.blocks/2):1))])
}