按另一个数组中的元素对结构数组进行排序

Question

I'm wanting to sort an array based off of another array. That probably sounds pretty confusing so let me explain.

Here is an example of an app about grocery shopping. I have an array like this:

var fruitsArray = [String:Int]()

Let's say that the values of the array are

[apple:32, banana:45, grape:7, strawberry:23]

First off, I sort this array by the Int , descendingly, which gives us

[banana:45 apple:32, strawberry:23, grape:7]

Ok great. But now I want an array of shopping lists and each element of that array contains an array of food. So let's make a Struct ...

struct List {
    var name:String = ""
    var items:[String] = [""]
    
    init(name: String, items: [String) {
        self.name = name
        self.items = items
    }
}

and then an array of List ...

var shoppingLists = [List]()

finally, let's add some elements to shoppingLists ...

[List(name: List 1, items: [banana, pizza, watermelon, apple]),
List(name: List 2, items: [cookie, water, grape, apple]),
List(name: List 3, items: [apple, strawberry, banana, cheese]),
List(name: List 4, items: [apple, strawberry, grape, watermelon])]

This is where it gets kind of difficult. I want to sort shoppingLists by looking at the items array in shoppingLists and comparing them with fruitsArray . Let me show you what I want the final product would be and then I'll explain why.

sortedShoppingList = 
[List(name: List 3, items: [apple, strawberry, banana, cheese]),
List(name: List 4, items: [apple, strawberry, grape, watermelon]),
List(name: List 1, items: [banana, pizza, watermelon, apple]),
List(name: List 2, items: [cookie, water, grape, apple])]

Why is it sorted like this? Let's take it element by element. So List 3 is at the top because it contains 3 elements from fruitsArray . Now you might be saying list 4 also contains 3 elements from fruitsArray and yes that's true, but list 3 contains elements from fruitsArray that are higher in "ranking". Both list 3 and 4 contain [apple, strawberry] but list 3 contains banana while list 4 contains grape . Banana outranksks" grape therefore making list 3 first. So moving on, List 1 is after list 4 because it contains [apple, banana] which is higher in "rank" than the [apple, grape] in list 2.

Answer 1

To tackle the problem I used a point system that would calculate points for each list in the shopping cart like so;

List 1, items: banana + pizza + watermelon + apple = 77   
List 2, items: cookie + water + grape + apple = 30    
List 3, items: apple + strawberry + banana + cheese = 100    
List 4, items: apple+ strawberry + grape + watermelon = 62

Then if we sort the point results we would get;

List 3, items: [apple + strawberry + banana] = 100   
List 1, items: [banana + apple] = 77   
List 4, items: [apple + strawberry + grape] = 62   
List 2, items: [grape + apple] = 30

But this is not the solution. We need to consider the number of fruits in each list and so we multiply point by items that match fruitArray like so;

List 3, items: [apple + strawberry + banana] = 100 * 3 = 300  
List 1, items: [banana + apple] = 77 * 2 = 154  
List 4, items: [apple + strawberry + grape] = 62  * 3 = 186  
List 2, items: [grape + apple] = 30 * 2 = 78

Now if we sort that we get the right result:

List 3, point = 300   
List 4, point = 186  
List 1, point = 154  
List 2, point = 78

Here is the code:

import UIKit

struct List {
    var id:Int = -1
    var items:[String] = [""]
    var point = 0

    init(id: Int, items: [String]) {
        self.id = id
        self.items = items
    }
}

var result = [List]()
var fruitsArray = ["banana":45, "apple":32, "strawberry":23, "grape":7]
var shoppingLists = [List(id: 1, items: ["banana", "pizza", "watermelon", "apple"]),
                     List(id: 2, items: ["cookie", "water", "grape", "apple"]),
                     List(id: 3, items: ["apple", "strawberry", "banana", "cheese"]),
                     List(id: 4, items: ["apple", "strawberry", "grape", "watermelon"])]


func calcPoints(lists: [List]){
    for list in lists{
        for item in list.items{
            let index = fruitsArray.index(forKey: item)
            if index != nil{
                shoppingLists[list.id - 1].point = shoppingLists[list.id - 1].point + fruitsArray[index!].value
            }
            else{
                shoppingLists[list.id - 1].items = shoppingLists[list.id - 1].items.filter { $0 != item }
            }
        }
        shoppingLists[list.id - 1].point = shoppingLists[list.id - 1].point * shoppingLists[list.id - 1].items.count
    }
}

calcPoints(lists: shoppingLists)
result = shoppingLists.sorted(by: { $0.point > $1.point })
print(result)

Answer 2

Use reduce function to calculate rank of each List and sorted method to sort an Array.

let sorted = shoppingLists.sorted { list1, list2 in
    let a = list1.items.reduce(0) { sum, nextItem in
        return sum + (fruitsArray[nextItem] ?? 0)
    }
    let b = list2.items.reduce(0) { sum, nextItem in
        return sum + (fruitsArray[nextItem] ?? 0)
    }
    return a > b
}