R/nearestNSitesFUN.R

In gmiskell/sensor_toolkit: Functions for Managing Sensor Networks

#' Find the Nearest n Sites.
#'
#' A function for finding the closest n sites to a location.
#' @param id Name of the location (as character string).
#' @param lat Latitude column.
#' @param lon Longitude column.
#' @param n Number of nearest sites to find.
#' @export
#' @examples
#' nearestNSitesFUN()


nearestNSitesFUN <- function(x, id, lat, lon, n){
  			
	library(sp); library(geosphere); library(rgeos); library(tidyverse)
	output.file <- NULL

	x$id <- x[[id]]; x$lat <- x[[lat]]; x$lon <- x[[lon]]

	x <- x %>%
		dplyr::select(id, lat, lon) %>%
		unique() %>%
		na.omit()
	suppressWarnings(rownames(x) <- seq(length = nrow(x)))

	sp.x = x
	coordinates(sp.x) <- ~lon+lat

	d <- suppressWarnings(distm(sp.x))
	min.distance <- apply(d, 2, function(x) order(x, decreasing = F)[2:(n+1)])

	for(i in 1:n){
		distance.i <- x[min.distance[i,],]
		combined.df <- cbind(x, distance.i)
		dist.min <- cbind(order = min.distance[i,], site = 		seq(length(min.distance[i,])))
		combined.df$dist <- d[dist.min]
		combined.df$order <- i
		colnames(combined.df) <- c(colnames(x), "n_id", "n_lat", "n_lon", "dist", "order")

		if(exists('output.file')){
			output.file <- rbind(output.file, combined.df)
			output.file <- unique(output.file)
		} else {
			output.file <- combined.df
		}
	}
	return(output.file)
}