Merge pull request #25 from rkukuh/dev

Add `countBy` extensions to Set and Dictionary

README.md

@@ -289,6 +289,30 @@ let countByResult = emails.countBy { (email) -> String in
 print(countByResult) // // ["gmail.com": 2, "yahoo.com": 1]
 ```
 
+#### Dictionary
+
+```swift
+let userAges = ["Alice": 30, "Bob": 28, "Carlos": 30, "David": 28]
+
+let countByResult = userAges.countBy { (name, age) -> Int in
+    return age
+}
+
+print(countByResult) // [28: 2, 30: 2]
+```
+
+#### Set
+
+```swift
+let emails: Set = ["[email protected]", "[email protected]", "[email protected]"]
+
+let countByResult = emails.countBy { (email) -> String in
+    return (email as! String).components(separatedBy: "@").last ?? ""
+}
+
+print(countByResult) // ["gmail.com": 2, "yahoo.com": 1]
+```
+
 ### `sum`
 
 The `sum` method returns the sum of all items in the collection.

Sources/SwiftCollections/CountBy/DictionaryCountByExtensions.swift

@@ -0,0 +1,17 @@
+//
+//  DictionaryCountByExtensions.swift
+//  
+//
+//  Created by R. Kukuh on 08/04/23.
+//
+
+import Foundation
+
+public extension Dictionary {
+    func countBy<T: Hashable>(_ transform: (Key, Value) -> T) -> [T: Int] {
+        return reduce(into: [:]) { (counts, keyValue) in
+            let key = transform(keyValue.key, keyValue.value)
+            counts[key, default: 0] += 1
+        }
+    }
+}

Sources/SwiftCollections/CountBy/SetCountByExtensions.swift

@@ -0,0 +1,17 @@
+//
+//  SetCountByExtensions.swift
+//  
+//
+//  Created by R. Kukuh on 08/04/23.
+//
+
+import Foundation
+
+public extension Set {
+    func countBy<T: Hashable>(_ transform: (Element) -> T) -> [T: Int] {
+        return reduce(into: [:]) { (counts, element) in
+            let key = transform(element)
+            counts[key, default: 0] += 1
+        }
+    }
+}

Tests/SwiftCollectionsTests/CountBy/ArrayCountByTests.swift

@@ -20,6 +20,7 @@ class ArrayCountByTests: XCTestCase {
 
     func testArrayCountByClosure() {
         let emails = ["[email protected]", "[email protected]", "[email protected]"]
+
         let countByResult = emails.countBy { (email) -> String in
             return email.components(separatedBy: "@").last ?? ""
         }

Tests/SwiftCollectionsTests/CountBy/DictionaryCountByTests.swift

@@ -0,0 +1,21 @@
+//
+//  DictionaryCountByTests.swift
+//  
+//
+//  Created by R. Kukuh on 08/04/23.
+//
+
+import XCTest
+@testable import SwiftCollections
+
+class DictionaryCountByClosureTests: XCTestCase {
+    func testDictionaryCountByClosure() {
+        let userAges = ["Alice": 30, "Bob": 28, "Carlos": 30, "David": 28]
+        let countByResult = userAges.countBy { (name, age) -> Int in
+            return age
+        }
+
+        XCTAssertEqual(countByResult[30], 2, "The count for age '30' should be 2")
+        XCTAssertEqual(countByResult[28], 2, "The count for age '28' should be 2")
+    }
+}

Tests/SwiftCollectionsTests/CountBy/SetCountByTests.swift

@@ -0,0 +1,22 @@
+//
+//  SetCountByTests.swift
+//  
+//
+//  Created by R. Kukuh on 08/04/23.
+//
+
+import XCTest
+@testable import SwiftCollections
+
+class SetCountByClosureTests: XCTestCase {
+    func testSetCountByClosure() {
+        let emails: Set = ["[email protected]", "[email protected]", "[email protected]"]
+
+        let countByResult = emails.countBy { (email) -> String in
+            return (email as! String).components(separatedBy: "@").last ?? ""
+        }
+
+        XCTAssertEqual(countByResult["gmail.com"], 2, "The count for 'gmail.com' should be 2")
+        XCTAssertEqual(countByResult["yahoo.com"], 1, "The count for 'yahoo.com' should be 1")
+    }
+}