R/x3p_average.R

In x3ptools: Tools for Working with 3D Surface Measurements

#' Average an x3p object
#' 
#' Calculate blockwise summary statistics on the surface matrix of an x3p.
#' @param x3p x3p object
#' @param b positive integer value, block size
#' @param f function aggregate function
#' @param ... parameters passed on to function f. Make sure to use na.rm = T as needed.
#' @export
#' @importFrom dplyr group_by summarize
#' @examples
#' logo <- x3p_read(system.file("csafe-logo.x3p", package="x3ptools"))
#' small <- x3p_average(logo)
x3p_average <- function(x3p, b = 10, f = mean, ...) {
  stopifnot("x3p" %in% class(x3p))
  x <- y <- value <- NULL # pass R CMD CHECK
    
  df <- x3p_to_df(x3p)
  scale <- x3p_get_scale(x3p)
  df$x <- round(df$x/scale,0)
  df$y <- round(df$y/scale,0)
  # round x and y to block size
  df$x <- df$x %/% b
  df$y <- df$y %/% b
 # browser()
  df <- summarize(group_by(df, x, y),
      value = f(value, ...)
    )
  # scale x and y back
  df$x <- df$x * scale * b
  df$y <- df$y * scale * b
  df_to_x3p(df)
}