R/methods-fapply.R

In gagolews/FuzzyNumbers: Tools to Deal with Fuzzy Numbers

## This file is part of the FuzzyNumbers package
##
## Copyright 2012-2019 Marek Gagolewski
##
##
## FuzzyNumbers is free software: you can redistribute it and/or modify
## it under the terms of the GNU Lesser General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
##
## FuzzyNumbers is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
## GNU Lesser General Public License for more details.
##
## You should have received a copy of the GNU Lesser General Public License
## along with FuzzyNumbers. If not, see <http://www.gnu.org/licenses/>.



#' @title
#' Apply a Function on a Fuzzy Number
#'
#' @description
#' Applies a given monotonic function
#' using the extension principle (i.e. the function is applied on alpha-cuts).
#'
#' @details
#' Currently only a method for the \linkS4class{PiecewiseLinearFuzzyNumber}
#' class has been defined. The computations are exact (up to a numeric error)
#' at knots. So, make sure you have a sufficient number of knots if you
#' want good approximation.
#'
#' For other types of fuzzy numbers, consider using
#' \code{\link{piecewiseLinearApproximation}}.
#'
#'
#' @param object a fuzzy number
#' @param fun a monotonic, vectorized R function
#' @param ... additional arguments passed to \code{fun}
#' 
#' @return Returns a \linkS4class{PiecewiseLinearFuzzyNumber}.
#'
#' @usage
#' \S4method{fapply}{PiecewiseLinearFuzzyNumber,function}(object, fun, ...)
#'
#' @docType methods
#' @name fapply
#' @rdname fapply-methods
#' @family PiecewiseLinearFuzzyNumber-method
#' @family extension_principle
#' @exportMethod fapply
#' @aliases fapply,PiecewiseLinearFuzzyNumber,function-method
setGeneric("fapply",
           function(object, fun, ...) standardGeneric("fapply"))



setMethod(
   f="fapply",
   signature(object="PiecewiseLinearFuzzyNumber", fun="function"),
   definition=function(object, fun, ...)
   {
      ol <-     c(object@a1, object@knot.left,  object@a2)
      or <- rev(c(object@a3, object@knot.right, object@a4))

      ol <- fun(ol, ...)
      or <- fun(or, ...)

      # using the extension principle and interval-based arithmetic operations
      PiecewiseLinearFuzzyNumber(knot.alpha=object@knot.alpha,
                                 knot.left=pmin(ol, or),
                                 knot.right=rev(pmax(ol, or))
      )
   }
)