Array groupedBy Extension

groupedByTests.swift

import Foundation
import XCTest

extension Array {
    func groupedByA<Key: Hashable>(mappingClosure: (Element) -> Key?) -> [Key: [Element]] {
        return reduce([:]) { (groupedBy, element) in
            guard let key = mappingClosure(element) else {
                return groupedBy
            }
            var groupedBy = groupedBy
            groupedBy[key] = groupedBy[key] ?? [Element]()
            groupedBy[key]?.append(element)
            return groupedBy
        }
    }
    
    func groupedByB<Key: Hashable>(mappingClosure: (Element) -> Key?) -> [Key: [Element]] {
        var groupedBy: [Key: [Element]] = [:]
        forEach { element in
            if let key = mappingClosure(element) {
                groupedBy[key] = groupedBy[key] ?? [Element]()
                groupedBy[key]?.append(element)
            }
        }
        return groupedBy
    }
}

extension String {
    static func randomAlphanumericString(length: Int) -> String {
        let letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".characters
        let lettersLength = UInt32(letters.count)
        let randomCharacters = (0..<length).map { i -> String in
            let offset = Int(arc4random_uniform(lettersLength))
            let c = letters[letters.startIndex.advancedBy(offset)]
            return String(c)
        }
        return randomCharacters.joinWithSeparator("")
    }
}

extension Int {
    static func random(max: UInt32) -> Int {
        return Int(arc4random_uniform(max))
    }
}

extension Bool {
    static func random() -> Bool {
        return arc4random_uniform(1) > 0
    }
}

class Test: XCTestCase {
    struct Person {
        var name: String
        var age: Int?
    }
    
    lazy var persons: [Person] = {
        var persons: [Person] = []
        for _ in 0...100000 {
            let length = Int.random(20)
            let name = String.randomAlphanumericString(length)
            let age = Int.random(99)
            let person = Person(name: name, age: age)
            persons.append(person)
        }
        return persons
    }()
    
    func testA() {
        measureBlock {
            self.persons.groupedByA { $0.name.characters.first }
        }
    }
    
    func testB() {
        measureBlock {
            self.persons.groupedByB { $0.name.characters.first }
        }
    }
}

Test Suite 'All tests' started at 2016-05-13 10:49:24.949
Test Suite 'GroupedByTests.xctest' started at 2016-05-13 10:49:24.950
Test Suite 'Test' started at 2016-05-13 10:49:24.951
Test Case '-[GroupedByTests.Test testA]' started.
GroupedByTests.swift:86: Test Case '-[GroupedByTests.Test testA]' measured [Time, seconds] average: 4.866, relative standard deviation: 30.558%, values: [9.325309, 4.356858, 4.313964, 4.359974, 4.352255, 4.455384, 4.371096, 4.324231, 4.436787, 4.365156], performanceMetricID:com.apple.XCTPerformanceMetric_WallClockTime, baselineName: "", baselineAverage: , maxPercentRegression: 10.000%, maxPercentRelativeStandardDeviation: 10.000%, maxRegression: 0.100, maxStandardDeviation: 0.100
Test Case '-[GroupedByTests.Test testA]' passed (48.932 seconds).
Test Case '-[GroupedByTests.Test testB]' started.
GroupedByTests.swift:92: Test Case '-[GroupedByTests.Test testB]' measured [Time, seconds] average: 3.817, relative standard deviation: 38.830%, values: [8.261461, 3.290685, 3.328974, 3.281495, 3.315450, 3.381211, 3.335369, 3.346904, 3.289857, 3.333601], performanceMetricID:com.apple.XCTPerformanceMetric_WallClockTime, baselineName: "", baselineAverage: , maxPercentRegression: 10.000%, maxPercentRelativeStandardDeviation: 10.000%, maxRegression: 0.100, maxStandardDeviation: 0.100
Test Case '-[GroupedByTests.Test testB]' passed (38.419 seconds).
Test Suite 'Test' passed at 2016-05-13 10:50:52.303.
Executed 2 tests, with 0 failures (0 unexpected) in 87.351 (87.353) seconds