R/bandwidth_nrd.R

In mpjashby/sfhotspot: Hot-Spot Analysis with Simple Features

#' Choose bandwidth for kernel-density estimation using a rule of thumb
#'
#' The code here is identical to that in \code{\link[MASS]{bandwidth.nrd}}
#'
#' @param data \code{\link[sf]{sf}} data frame containing points.
#'
#' @return A single numeric value giving the chosen bandwidth.
#'
#' @noRd

bandwidth_nrd_sf <- function(data) {

  coords <- suppressWarnings(sf::st_coordinates(data))

  mean(bandwidth_nrd(coords[, 1]), bandwidth_nrd(coords[, 2]))

}

bandwidth_nrd <- function(x) {

  r <- stats::quantile(x, c(0.25, 0.75))
  h <- (r[2] - r[1]) / 1.34
  4 * 1.06 * min(sqrt(stats::var(x)), h) * length(x) ^ (-1 / 5)

}