Filter two struct arrays-CodePudding

What is the best way to filter two Struct Arrays to match by ID and added the information in a specific property.

Example

Struct User {
    let id: Int
    let name: String
    var arts: [Article]?
}

Struct Article {
    let userId: Int
    let id: Int
    let title: String
    let body: String
}

I have an array with all Users and other array with all Post for all Users. I need to add into User Array all post by user (User.id == Article.userId)

I'm trying to do with this.

var art = [Article]()
var users = [User]()

self?.art.forEach({ art in
                guard let userId = self?.users.firstIndex(where: { $0.id == art.userId }) else {
                    print("Failed to find a Art by UserID")
                    return
                }
                self?.users[userId].arts?.append(art)
            })

The idea is added into User Struct all Articles corresponding by user

CodePudding user response：

class Article {
    let userId: Int
    let id: Int
    let title: String
    let body: String
}

class User {
    let id: Int
    let name: String
    var arts: [Post]?
}

I think the best possible way is to convert it to a dictionary. I think the below code is well explonary.

var dict = [Int: [Article]]()

var arts = [Article]()

for art in arts {
  dict[art.userId, default: []].append(art)
}

var users = [User]()

for case let user in users {
   let articles = dict[user.id]
   user.atrs = articles
}

CodePudding user response：

the variable users is used to contain elements of type Article?

CodePudding user response：

I think your code was in the right direction. Try this approach (works for me):

var arts = [Article(userId: 1, id: 1, title: "title1"),
            Article(userId: 6, id: 1, title: "title6")]

var users = [User(id: 1, name: "user1"),
             User(id: 2, name: "user2")]

print("---> before users: \n \(users)")

arts.forEach{ art in
    if let userNdx = users.firstIndex(where: { $0.id == art.userId }) {
        if let _ = users[userNdx].arts {} else {
            users[userNdx].arts = []
        }
        
        users[userNdx].arts!.append(art)
    }
}

print("\n---> after users: \n \(users)")