Grouping an array by members in Swift

Group.swift

import Foundation

extension Array {
	
	func group<Discrimininator>(by discriminator: (Element)->(Discrimininator)) -> [Discrimininator: [Element]] where Discrimininator: Hashable {
		
		var result = [Discrimininator: [Element]]()
		for element in self {
			
			let key = discriminator(element)
			var array = result[key] ?? [Element]()
			array.append(element)
			result[key] = array
		}
		
		return result
	}
}


struct Name {
	let first: String
	let last: String
}

let names = [
	Name(first: "Alice", last: "Smith"),
	Name(first: "Bob", last: "Jones"),
	Name(first: "Colin", last: "Smith"),
	Name(first: "Alice", last: "Williams"),
]

print(names.group { $0.last })
// ["Jones": [Name(first: "Bob", last: "Jones")], "Williams": [Name(first: "Alice", last: "Williams")], "Smith": [Name(first: "Alice", last: "Smith"), Name(first: "Colin", last: "Smith")]]

print(names.group { $0.first })
// ["Bob": [Name(first: "Bob", last: "Jones")], "Alice": [Name(first: "Alice", last: "Smith"), Name(first: "Alice", last: "Williams")], "Colin": [Name(first: "Colin", last: "Smith")]]

print(names.group { $0.first.characters.count })
//[5: [Name(first: "Alice", last: "Smith"), Name(first: "Colin", last: "Smith"), Name(first: "Alice", last: "Williams")], 3: [Name(first: "Bob", last: "Jones")]]