lab6/R/knapsack_greedy.R

In KarthiKeyanD4/lab6r: Knapsack Functions

#' The knapsack - Greedy Algorithm
#' 
#' @description knapsack - Greedy Algorithm
#'
#' @param x as dataframe
#' @param W as numeric
#' @param fast as logical
#'
#' @return list containing value and elements
#' @export greedy_knapsack
#' @useDynLib lab6
#' @import Rcpp 

  greedy_knapsack <- function(x,W, fast = FALSE ){

  if(is.numeric(W)== F || is.data.frame(x) ==F){
    stop("Please enter valid inputs")
  }
  else if(W <= 0){
    stop("Please enter weight larger than 0")
  }
  require(Rcpp)
  cppFunction("double  vectorSum(NumericVector x){
        return std::accumulate(x.begin(), x.end(), 0.0);
    }")

  x$elements <- as.numeric(rownames(x))
  x$vw <- x$v/x$w
  x <- x[order(-x$vw),]
  x <- x[which(x$w <= W),]
  x$weight_sum <- cumsum(x$w)
  x <- x[which(x$weight_sum <= W),]
  if(fast == TRUE){
    knapsackvalue <- vectorSum(x$v)
  }else{
  knapsackvalue <- sum(x$v)
  }
  elements <- x$elements

   result <- list("value" = round(knapsackvalue), "elements" = elements)
   return(result)

  }
#RNGkind(sample.kind = "Rounding")
#set.seed(42)
#n <- 2000
#knapsack_objects <- data.frame(w=sample(1:4000, size = n, replace = TRUE), v=runif(n = n, 0, 10000))
#greedy_knapsack(x = knapsack_objects[1: 8,], W = 3500, fast=TRUE)