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#' PR (landscape level)
#'
#' @description Patch richness (Diversity metric)
#'
#' @param landscape A categorical raster object: SpatRaster; Raster* Layer, Stack, Brick; stars or a list of SpatRasters.
#'
#' @details
#' \deqn{PR = m}
#' where \eqn{m} is the number of classes
#'
#' PR is a 'Diversity metric'. It is one of the simplest diversity and composition measures.
#' However, because of its absolute nature, it is not comparable among landscapes with
#' different total areas.
#'
#' \subsection{Units}{None}
#' \subsection{Range}{PR >= 1}
#' \subsection{Behaviour}{Equals PR = 1 when only one patch is present and increases, without
#' limit, as the number of classes increases}
#'
#' @return tibble
#'
#' @examples
#' landscape <- terra::rast(landscapemetrics::landscape)
#' lsm_l_pr(landscape)
#'
#' @aliases lsm_l_pr
#' @rdname lsm_l_pr
#'
#' @references
#' McGarigal K., SA Cushman, and E Ene. 2023. FRAGSTATS v4: Spatial Pattern Analysis
#' Program for Categorical Maps. Computer software program produced by the authors;
#' available at the following web site: https://www.fragstats.org
#'
#' @export
lsm_l_pr <- function(landscape){
landscape <- landscape_as_list(landscape)
result <- lapply(X = landscape,
FUN = lsm_l_pr_calc)
layer <- rep(seq_along(result),
vapply(result, nrow, FUN.VALUE = integer(1)))
result <- do.call(rbind, result)
tibble::add_column(result, layer, .before = TRUE)
}
lsm_l_pr_calc <- function(landscape){
richness <- length(get_unique_values_int(landscape, verbose = FALSE))
# all values NA
if (richness == 0) {
return(tibble::tibble(level = "landscape",
class = as.integer(NA),
id = as.integer(NA),
metric = "pr",
value = as.double(NA)))
}
return(tibble::tibble(level = "landscape",
class = as.integer(NA),
id = as.integer(NA),
metric = "pr",
value = as.double(richness)))
}
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