R/AUC_of_cross_function.R

In TrigosTeam/SPIAT: Spatial Image Analysis of Tissues

#' The difference in AUC of the cross function curves
#'
#' @description Calculate the difference of area under the curve (AUC) between
#'   two curves, normalised by the total area of the graph.

#' @param df.cross Data.frame. The output of
#'   \code{\link{calculate_cross_functions}}. Containing the positions of the
#'   two curves. Columns contain "r", "border" and "theo".
#' @return A number
#' @export
#'
#' @examples
#' df_cross <- calculate_cross_functions(SPIAT::defined_image, method = "Kcross",
#'               cell_types_of_interest = c("Tumour","Immune3"),
#'               feature_colname ="Cell.Type", dist = 100)
#' AUC_of_cross_function(df_cross)

AUC_of_cross_function <- function(df.cross){
    AUC <- pracma::trapz(df.cross$r ,df.cross$border) - 
        pracma::trapz(df.cross$r,df.cross$theo)
    
    # get the cross k result image size
    X <- max(df.cross$r)
    Y <- max(c(df.cross$theo, df.cross$border))
    
    # calculate normalised AUC
    n_AUC <- AUC/(X*Y)
    return(n_AUC)
}