R/xlWC.R

In xinye1/xltools: Xinye Li's R Toolkit

#' Week commencing date
#'
#' Find the week commencing of a date, given a specific day as the start of week.
#'
#'
#' @param date Date value for which the week start date can be found.
#'   Default is \code{\link{Sys.Date}}
#' @param pre_wk Integer for the number of weeks prior to the lookup date.
#'   Default is 0, no shifting of the week.
#' @param wk_start Integer, possible values are 1 - 7, correspnoding to Monday to Sunday as
#'   the start of the week. Default is 1 for Monday.
#' @param format A string for date output format, could be e.g. \code{'\%Y\%m\%d'}. If left
#' NULL then the output is of \code{Date} class.
#' # Get the Sunday before 2 weeks prior to 1st Jan 2017
#' xlWC(as.Date('2017-01-01'), pre_wk = 2, wk_start = 7)
#'
#'
#' @import dplyr
#' @export
xlWC <- function(date = Sys.Date(), pre_wk = 0, wk_start = 1, format = NULL) {
  weekday <- date %>% as.POSIXlt %>% '$'(wday)
  weekday[weekday == 0] <- 7
  weekday <- (weekday - wk_start) %% 7
  wc <- date - weekday - pre_wk * 7
  if (!is.null(format)) {
    wc <- format(wc, format = format)
  }
  return(wc)
}