R/latitudinalMean.R

In climateStability: Estimating Climate Stability from Climate Model Data

#' @title latitudinalMean
#'
#' @description A function to calculate mean values of a raster at every line of latitude, at the resolution of a given raster layer. Put another way, for each row in the raster, it calculates a mean.
#'
#' @param rasterForCalculation A raster that contains data for plotting according to latitudinal value
#'
#' @return A vector of raster values for each absolute value of latitude.
#'
#' @keywords manip
#'
#' @references
#' Owens, H.L., Guralnick, R., 2019. climateStability: An R package to estimate
#' climate stability from time-slice climatologies. Biodiversity Informatics
#' 14, 8–13. https://doi.org/10.17161/bi.v14i0.9786
#'
#' @seealso \code{\link{absLatitudinalMean}} to calculate mean value for each absolute value of latitude.
#'
#' @examples
#'
#' precipDeviation <- terra::rast(system.file("extdata/precipDeviation.asc",
#'                                             package = "climateStability"))
#' precipStability <- 1/precipDeviation
#' latMean <- latitudinalMean(rasterForCalculation = precipStability)
#' plot(latMean, main = "Precipitation Stability by Latitude",
#' ylab = "Relative Stability", type = "l")
#'
#' @importFrom terra as.points crds
#' @importFrom methods is
#'
#' @export
latitudinalMean <- function(rasterForCalculation){
  if (!is(rasterForCalculation, "SpatRaster")){
    warning("Supplied argument is not a SpatRaster./n", sep = "")
    return(NULL)
  }

  spatVect <- terra::as.points(rasterForCalculation)
  pointExtData <- cbind(as.data.frame(terra::crds(spatVect)),
                        as.data.frame(spatVect))
  latData <- matrix(nrow = length(unique(pointExtData$y)), ncol = 2)
  latData[,1] <- sort(unique(pointExtData$y))
  colnames(latData) <- c("Latitude",  "Value")
  lat <- sort(unique(pointExtData$y))
  count <- 1
  while(count <= length(lat)){
    latData[latData[,1]==lat[[count]],][2] <- c(
      mean(pointExtData[pointExtData$y==lat[[count]],3]))
    count <- count + 1
  }
  return(latData)
}