Merge pull request #37 from michaeleisel/added_minBy_and_maxBy_methods

Added minBy and maxBy methods

ExSwift/Array.swift

@@ -429,6 +429,56 @@ internal extension Array {
 
     }
 
+    /**
+        The value for which call(value) is highest.
+
+        :returns: Max value in terms of call(value)
+    */
+    func maxBy <U: Comparable> (call: (Element) -> (U)) -> Element? {
+
+        if let firstValue = self.first {
+            var maxElement: T = firstValue
+            var maxValue: U = call(firstValue)
+            for i in 1..<self.count {
+                let element: Element = self[i]
+                let value: U = call(element)
+                if value > maxValue {
+                    maxElement = element
+                    maxValue = value
+                }
+            }
+            return maxElement
+        } else {
+            return nil
+        }
+
+    }
+
+    /**
+        The value for which call(value) is lowest.
+
+        :returns: Min value in terms of call(value)
+    */
+    func minBy <U: Comparable> (call: (Element) -> (U)) -> Element? {
+
+        if let firstValue = self.first {
+            var maxElement: T = firstValue
+            var minValue: U = call(firstValue)
+            for i in 1..<self.count {
+                let element: Element = self[i]
+                let value: U = call(element)
+                if value < minValue {
+                    maxElement = element
+                    minValue = value
+                }
+            }
+            return maxElement
+        } else {
+            return nil
+        }
+
+    }
+
     /**
         Iterates on each element of the array.
 

ExSwiftTests/ExSwiftArrayTests.swift

@@ -395,4 +395,28 @@ class ExtensionsArrayTests: XCTestCase {
         let array1 = ["zero", "one", "two", "three"][rangeAsArray: 1...3]
         let array2 = ["zero", "one", "two", "three"][rangeAsArray: 1..<3]
     }
+
+    func testMinBy() {
+        var minValue: Int?
+        minValue = array.minBy({ -$0 })
+        XCTAssertEqual(minValue!, 5)
+        minValue = array.minBy({ $0 % 4 })
+        XCTAssertEqual(minValue!, 4)
+        minValue = array.minBy({ $0 })
+        XCTAssertEqual(minValue!, 1)
+        minValue = array.minBy({ $0 % 2 })
+        XCTAssertTrue(minValue! == 2 || minValue! == 4) // it's a tie
+    }
+
+    func testMaxBy() {
+        var maxValue: Int?
+        maxValue = array.maxBy({ -$0 })
+        XCTAssertEqual(maxValue!, 1)
+        maxValue = array.maxBy({ $0 % 4 })
+        XCTAssertEqual(maxValue!, 3)
+        maxValue = array.maxBy({ $0 })
+        XCTAssertEqual(maxValue!, 5)
+        maxValue = array.maxBy({ $0 % 3 })
+        XCTAssertTrue(maxValue! == 2 || maxValue! == 5) // it's a tie
+    }
 }