sub_set_years.R

#'
#'
#'
#' Helper function for selecting points for an axis so not all are necessary
#'
#' @description {
#' Takes an array and subsamples it every n places. Many times there are so many years the labels on 
#' the plot overlap. This function returns the position and label for 
#' the subset. The function can be used on any type of simple array.
#'}
#' @param years an array of years 
#' @return a list containing:
#' 	\code{position} array of axis positions
#' 	\code{label} array of labels
#' 	
#' @author Paul Whitfield <paul.h.whitfield@gmail.com>

#'
#' @export 
#' 
#' 
#' @example
#' myears <- c(1900:2045)
#' myears <-sub_set_Years(myears,20)
#' myears
#'
#' a <-LETTERS
#' my_alpha <- sub_set_Years(a,5)
#' my_alpha


sub_set_Years <- function(years,n) {
  
  pts <- c(1:length(years))
  pts<-pts[1:(length(years)/n)*n]
  
  years <- years[pts]
  
  result <- list(pts, years)
  names(result) <-c("position","label")
  return(result)
}