R/cusum_single_median.R

In johnmackintosh/cusumcharter: Easier CUSUM Control Charts

#' Calculates the cumulative sum statistic relative to target, or median value
#'
#' Calculates the cumulative sum statistic of a vector of values, centred on either the median of the data, or a supplied target value.
#'
#' @param x a numeric vector from which to calculate the cumulative sum statistics
#' @param target value to compare each element of x to. If not provided, the median value of x will be calculated and used as a target value
#'
#'
#' @return a vector of the cumulative sum statistic, centred on the target value
#' @export
#'
#' @examples
#'
#' test_vec <- c(0.175, 0.152, 0.15, 0.207, 0.136, 0.212, 0.166)
#' cusum_single_median(test_vec)
#'
cusum_single_median <- function(x, target = NULL) {
  stopifnot(is.numeric(x) | is.double(x) | is.integer(x))
  stopifnot(!is.na(x))
  stopifnot(is.numeric(target) | is.double(target) | is.integer(target) | is.null(target))

  target <-  if (is.null(target)) {target = stats::median(x, na.rm = TRUE)} else target
  si <- x - target
  cusumx <- cumsum(si)
  cusum_target <- cusumx + target
  return(cusum_target)

}