R/stat_index.R

In ggseas: 'stats' for Seasonal Adjustment on the Fly with 'ggplot2'

StatIndex <- ggproto("StatIndex", Stat, 
                          required_aes = c("x", "y"),
                          
                          compute_group = function(data, scales, 
                                                   index.ref, index.basis, ...) {
                             data <- data[order(data$x), ]
                             data$y <- index_help(data$y, ref = index.ref, 
                                                  basis = index.basis)
                             
                             result <- data.frame(x = data$x, y = data$y)
                             return(result)
                          }
)




#' Index Stat
#' 
#' Convert a time series from the original scale to an index for ggplot2
#' 
#' @export
#' @import ggplot2
#' @param index.ref if not NULL, a vector of integers indicating which elements of
#' the beginning of each series to use as a reference point for converting to an index.  
#' If NULL, no conversion takes place and the data are presented on the original scale.
#' @param index.basis if index.ref is not NULL, the basis point for converting
#' to an index, most commonly 100 or 1000.  See examples.
#' @param ... other arguments for the geom
#' @inheritParams ggplot2::stat_identity
#' @family time series stats for ggplot2
#' @examples
#' ap_df <- tsdf(AirPassengers)
#' 
#' ggplot(ldeaths_df, aes(x = YearMon, y = deaths, color = sex)) +
#'    stat_index(index.ref = 1:12, index.basis = 1000) +
#'    ylab("Deaths index\n(average of first 12 months = 1000")
#'    
stat_index <- function(mapping = NULL, data = NULL, geom = "line",
                       position = "identity", show.legend = NA, 
                       inherit.aes = TRUE, index.ref = NULL, 
                       index.basis = 100, ...) {
   ggplot2::layer(
      stat = StatIndex, data = data, mapping = mapping, geom = geom, 
      position = position, show.legend = show.legend, inherit.aes = inherit.aes,
      params = list(na.rm = FALSE, index.ref = index.ref, index.basis = index.basis, ...)
      # note that this function is unforgiving of NAs.
   )
}