Filter array of nested structs

Question

I'm looking for a nice swift solution for the following problem:

Lets say we have 2 structs like so:

struct Person {
    let name: String
    let age: Int
    let skills: Skills
    init(name: String, age: Int, skills: Skills) {
        self.name = name
        self.age = age
        self.skills = skills
    }

}

struct Skills {
    let canUseBow: Bool
    let canUseSword: Bool
    let canUseShield: Bool
    init(canUseBow: Bool, canUseSword: Bool, canUseShield: Bool) {
        self.canUseBow = canUseBow
        self.canUseSword = canUseSword
        self.canUseShield = canUseShield
    }
}

Now lets say I have an array of Person where each person has their own skills obviously where the corrosponding values can be true or false.

Lets say I want another array of just people that have the skill canUseBow as true so that skill must be set to true , how would I go about filtering out the Persons that do not have canUseBow set to true?

I was thinking in a direction of:

filteredPersons = persons.filter {
  $0.skills
}

But that way it would require me to than select something after skills for example $0.skills.canUseBow

That does not seem very future proof, lets say I would want to add more skills than I would also have to change the filter method again. Are there better ways to go about this?

I’m not following... what’s wrong with $0.skills.canUseBow? — aheze
– aheze, Commented Jun 20, 2021 at 18:50
What is your concern with filteredPersons = persons.filter { $0.skills.canUseBow } or filteredPersons = persons.filter { $0.skills.canUseBow == false } ? — Tarun Tyagi
– Tarun Tyagi, Commented Jun 20, 2021 at 18:50
The reason I figure this is not great because maybe a person has over 100 skills which I might want to filter lets say 50 I would need 50 different statements? I just doesn't seem very efficient. (I might be missing something) — Robin
– Robin, Commented Jun 20, 2021 at 18:57

Tarun Tyagi · Accepted Answer · 2021-06-20 19:32:39Z

3

You can try this with an OptionSet that can hold all of these flags for you in a simple Int storage.

import Foundation

struct Person {
    let name: String
    let age: Int
    let skills: Skills
    init(name: String, age: Int, skills: Skills) {
        self.name = name
        self.age = age
        self.skills = skills
    }
}

struct Skills: OptionSet {
    let rawValue: Int
    init(rawValue: Int) {
        self.rawValue = rawValue
    }
    
    static let canUseBow = Skills(rawValue: 1 << 0)
    static let canUseSword = Skills(rawValue: 1 << 1)
    static let canUseShield = Skills(rawValue: 1 << 2)
    
    init(json: [String: Bool]) {
        var skills = Skills(rawValue: 0)
        if let canUseBow = json["can_use_bow"], canUseBow {
            skills.insert(.canUseBow)
        }
        if let canUseSword = json["can_use_sword"], canUseSword {
            skills.insert(.canUseSword)
        }
        if let canUseShield = json["can_use_shield"], canUseShield {
            skills.insert(.canUseShield)
        }
        self = skills
    }
}

How to instantiate `Skills`?

let skills = Skills(json: [
    "can_use_bow" : true,
    "can_use_sword" : true,
    "can_use_shield" : false,
])

How to filter based on multiple skills?

let targetSkills: Skills = [.canUseBow, .canUseSword]

let persons: [Person] = []
let filteredPersons = persons.filter { 
    targetSkills.isSubset(of: $0.skills)
}

edited Jun 20, 2021 at 19:32

answered Jun 20, 2021 at 19:18

Tarun Tyagi

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1 Comment

Robin Over a year ago

Thank you so much! This works perfectly especially being able to provide it with the JSON is exactly what I'm looking for!

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