R/build_grid_identical.R

In rollply: Moving-Window Add-on for 'plyr'

#'
#' @title Build a regular grid
#'
#' @description Create a regular grid with the same number of points on each
#'              dimension.
#'
#' @param coords A matrix or data frame of coordinates as columns
#' @param npts The approximate total number of points of the output grid
#' @param pad Padding on each dimension (a positive number makes a grid
#'            that is larger than the ranges of the coordinates).
#' @param ... other arguments are silently ignored
#' 
#' @return The coordinates of a grid of points as a data frame with
#'         approximately \code{npts} rows and \code{ncol(coords)} columns. Names
#'         are transfered from the \code{coords} data frame.
#' 
#' @details This function creates a grid that covers a set of points. The 
#'          number of points of the output grid is the same on all dimensions. 
#'          This is probably the only useful option for 1D moving-window 
#'          computations.
#' 
#' @family grid building functions
#'
#' @export
#'

build_grid_identical <- function(coords, npts, pad = 0, ...) {

  build_grid_check_vars(coords, npts)

  coords.ranges <- apply(coords, 2, range)
  ndims <- ncol(coords)

  # The input npts is the *total* number of points wanted so we need ^(1/ndims)
  # so we use the correct, identical amount of points on each dimension.
  length.onedim <- floor(npts^(1/ndims))

  grid.seed <- sapply(seq.int(ncol(coords)),
                      build_grid_seed_onedim, coords.ranges, length.onedim, pad,
                      simplify = FALSE)
  names(grid.seed) <- colnames(coords)

  return( expand.grid(grid.seed, KEEP.OUT.ATTRS = FALSE) )
}