zmjones

decay <- function(yvar, d) {
  # yvar: a binary variable
  # d: number of periods
  # returns: the cumulative sum of yvar at each point
  # where each addition to the count decays away after d periods
  yvar[is.na(yvar)] <- 0
  run <- cumsum(yvar)
  tvar <- seq_along(yvar)
  run <- 0
  sum <-  0