R 中的背包问题：如何在 R 中使用循环来检查每个项目而不是整列

Question

我一直在我的大学学习“模拟”课程，现在有一个解决背包问题的任务。基本上我有 3 个运输车（g1、g2、g3），每个运输车都可以承载不同的重量，最重要的是你可以将每个物品放入一个运输车中 5 次。我的想法是使用 while 循环，这样只要总重量低于最大重量，它就会运行。并且程序会首先选择具有最高关系的项目，只要它们的选择索引不等于 0。但是在这里我被卡住了，它似乎在每个循环中一次获取列的所有项目，并且当值超过最大值时也不会停止（最后 returns weight = 748）。

因此：我如何让循环只检查每个项目而不是整列，我如何确保它不超过重量限制？

非常感谢您的提前帮助！！

WeightIndex<- c(2, 3, 4, 1, 7, 5, 8, 15, 9, 11) #indexing the weight of each item
WorthIndex <-c(3, 4, 5, 1, 3, 7, 3, 21, 11, 10)#indexing the worth of each item
Relation <- WorthIndex/WeightIndex #creates a relation between weight/worth of the item
PickIndex <- rep(5,10) #each item can be picked 5 times


Items <-cbind(ItemIndex, WeightIndex, WorthIndex, Relation, PickIndex) #binding the indexes to a matrix


g1 <- 300 #Max weight of carrier 1
g2 <- 250 #max weight of carrier 2
g3 <- 200 #max weight of carrier 3

ItemsSorted<-Items[order(Items[,4],decreasing=TRUE),] #Sorts the items after the highest Relation of weight to worth

ItemsSorted1 <- ItemsSorted #creates a copied matrix for the first loop

TWE1 <-0#Total Weight  of carrier 1

TWO1 <-0 #total worth  of carrier 1


print (ItemsSorted1) #bug check

while (TWE1 <= g1){    #while the condition is true, the program should execute a for loop
  

    if(ItemsSorted1[,5]!= 0) #in theory the loop should go bottom down and take the items with the highest price/weight relation first and it should only take items whose pick-index doesnt equal 0
      {  
   TWE1<-TWE1+ItemsSorted1[,2] #the weight of the taken item gets appended to the list of the total weight
   TWO1 <-TWO1 + ItemsSorted1[,3] #the worth of the taken item gets appended to the list of total worth
    ItemsSorted1[,5] <- ItemsSorted1[,5] - 1 #deducts 1 from the pick- Index as the item has been taken
    TWE1 <- sum(TWE1) #turns the list into one number
    TWO1 <- sum(TWO1) #turns the list into one number
    print(TWE1)    #bug check
    }
  
}


print(paste("Total weight C1",TWE1))
print(paste("Total worth C1",TWO1))
print(ItemsSorted1)```

Answer 1

略读您的代码，您似乎缺少某种方法来索引您在 ItemsSorted1 矩阵中引用的数字。您在 while 语句后的评论说您希望代码成为运行一个 for 循环，但正如所写的那样，它没有要递增的变量。

您可以执行类似以下的操作来获得预期的行为：

i <- 1 # create row-id variable to keep track of position in ItemsSorted1

while (TWE1 <= g1){    
   if(ItemsSorted1[i,5]!= 0){ # go item by item through the sorted list;
      TWE1<-TWE1+ItemsSorted1[i,2] #the weight of the taken item gets appended to the list of the total weight
      TWO1 <-TWO1 + ItemsSorted1[i,3] #the worth of the taken item gets appended to the list of total worth
      ItemsSorted1[i,5] <- ItemsSorted1[i,5] - 1 #deducts 1 from the pick- Index as the item has been taken
      TWE1 <- sum(TWE1) #turns the list into one number
      TWO1 <- sum(TWO1) #turns the list into one number
      print(TWE1)    #bug check
   }
   else if (i<nrow(ItemsSorted1){
      i <- i+1 
   }else{
      break
   }
}

R 中的背包问题：如何在 R 中使用循环来检查每个项目而不是整列

Knapsack problem in R: How to use loop in R to check for each item instead of whole column

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