diff --git a/Sources/DataStructures/Pair/Pair.swift b/Sources/DataStructures/Pair/Pair.swift
index ba978cc..2c512b4 100644
--- a/Sources/DataStructures/Pair/Pair.swift
+++ b/Sources/DataStructures/Pair/Pair.swift
@@ -32,3 +32,14 @@ public protocol Pair {
     /// Creates a `Pair` with the given values.
     init(_ a: A, _ b: B)
 }
+
+extension Pair {
+
+    // MARK: - Instance Methods
+
+    /// - Returns: A `Pair` with its members transformed by the given function.
+    public func map <P,C,D> (_ f: (A,B) -> (C,D)) -> P where P: Pair, P.A == C, P.B == D {
+        let (c,d) = f(self.a, self.b)
+        return P(c,d)
+    }
+}
diff --git a/Sources/DataStructures/Pair/SymmetricPair.swift b/Sources/DataStructures/Pair/SymmetricPair.swift
index f4f5251..ba556a9 100644
--- a/Sources/DataStructures/Pair/SymmetricPair.swift
+++ b/Sources/DataStructures/Pair/SymmetricPair.swift
@@ -17,3 +17,13 @@ extension SymmetricPair where A: Equatable {
         return a == value || b == value
     }
 }
+
+extension SymmetricPair {
+
+    // MARK: - Instance Methods
+
+    /// - Returns: A `SymmetricPair` with its members transformed by the given function.
+    public func map <P,C> (_ f: (A) -> C) -> P where P: SymmetricPair, P.A == C {
+        return P(f(self.a), f(self.b))
+    }
+}
diff --git a/Tests/AlgorithmsPerformanceTests/XCTestManifests.swift b/Tests/AlgorithmsPerformanceTests/XCTestManifests.swift
index 379bca3..dc63c09 100644
--- a/Tests/AlgorithmsPerformanceTests/XCTestManifests.swift
+++ b/Tests/AlgorithmsPerformanceTests/XCTestManifests.swift
@@ -2,7 +2,7 @@ import XCTest
 
 extension StableSortPerformanceTests {
     static let __allTests = [
-        ("testStableSort", testStableSort_O_nlogn),
+        ("testStableSort_O_nlogn", testStableSort_O_nlogn),
     ]
 }
 
diff --git a/Tests/DataStructuresTests/CrossTests.swift b/Tests/DataStructuresTests/CrossTests.swift
index 071d359..97b1d7a 100644
--- a/Tests/DataStructuresTests/CrossTests.swift
+++ b/Tests/DataStructuresTests/CrossTests.swift
@@ -30,4 +30,13 @@ class CrossTests: XCTestCase {
         XCTAssertFalse(a < b)
         XCTAssertFalse(b > a)
     }
+    
+    func testMap() {
+        let start = Cross("a",2)
+        let expected = Cross(4,"aa")
+        let function: (String,Int) -> (Int,String) = { string, int in
+            (int*2, string+string)
+        }
+        XCTAssertEqual(start.map(function),expected)
+    }
 }
diff --git a/Tests/DataStructuresTests/PairTests/OrderedPairTests.swift b/Tests/DataStructuresTests/PairTests/OrderedPairTests.swift
new file mode 100644
index 0000000..3076e34
--- /dev/null
+++ b/Tests/DataStructuresTests/PairTests/OrderedPairTests.swift
@@ -0,0 +1,18 @@
+//
+//  OrderedPairTests.swift
+//  Structure
+//
+//  Created by Benjamin Wetherfield on 15/11/2018.
+//
+
+import XCTest
+import DataStructures
+
+class OrderedPairTests: XCTestCase {
+    
+    func testMap() {
+        let start = OrderedPair("a","ab")
+        let expected = OrderedPair(1,2)
+        XCTAssertEqual(start.map { $0.count }, expected)
+    }
+}
diff --git a/Tests/DataStructuresTests/UnorderedPairTests.swift b/Tests/DataStructuresTests/PairTests/UnorderedPairTests.swift
similarity index 91%
rename from Tests/DataStructuresTests/UnorderedPairTests.swift
rename to Tests/DataStructuresTests/PairTests/UnorderedPairTests.swift
index 72f4173..7473a3b 100644
--- a/Tests/DataStructuresTests/UnorderedPairTests.swift
+++ b/Tests/DataStructuresTests/PairTests/UnorderedPairTests.swift
@@ -58,6 +58,12 @@ class UnorderedPairTests: XCTestCase {
             }
         }
     }
+    
+    func testMap() {
+        let start = UnorderedPair("a","ab")
+        let expected = UnorderedPair(1,2)
+        XCTAssertEqual(start.map { $0.count }, expected)
+    }
 }
 
 func randomString(maxLength: Int = 10) -> String {
diff --git a/Tests/DataStructuresTests/XCTestManifests.swift b/Tests/DataStructuresTests/XCTestManifests.swift
index 93bf0c9..afb0dcf 100644
--- a/Tests/DataStructuresTests/XCTestManifests.swift
+++ b/Tests/DataStructuresTests/XCTestManifests.swift
@@ -35,6 +35,8 @@ extension ArrayExtensionsTests {
 
 extension BimapTests {
     static let __allTests = [
+        ("testCompose", testCompose),
+        ("testComposeOperator", testComposeOperator),
         ("testInitEmpty", testInitEmpty),
         ("testKeySubscript", testKeySubscript),
         ("testRemoveAll", testRemoveAll),
@@ -43,8 +45,6 @@ extension BimapTests {
         ("testUpdateKey", testUpdateKey),
         ("testUpdateValue", testUpdateValue),
         ("testValueSubscript", testValueSubscript),
-        ("testCompose", testCompose),
-        ("testComposeOperator", testComposeOperator),
     ]
 }
 
@@ -53,7 +53,7 @@ extension BinaryHeapTests {
         ("testBalance", testBalance),
         ("testBasicInsertPop", testBasicInsertPop),
         ("testPopNil", testPopNil),
-        ("testSimpleBalance", testSimpleBalance)
+        ("testSimpleBalance", testSimpleBalance),
     ]
 }
 
@@ -110,6 +110,7 @@ extension CrossTests {
         ("testComparableFalseEqual", testComparableFalseEqual),
         ("testComparableLexicographic", testComparableLexicographic),
         ("testComparableLexicographicFalse", testComparableLexicographicFalse),
+        ("testMap", testMap),
     ]
 }
 
@@ -282,6 +283,12 @@ extension OrderedDictionaryTests {
     ]
 }
 
+extension OrderedPairTests {
+    static let __allTests = [
+        ("testMap", testMap),
+    ]
+}
+
 extension PairsTests {
     static let __allTests = [
         ("testPairs", testPairs),
@@ -517,6 +524,7 @@ extension UnorderedPairTests {
         ("testManyHashValuesIntForCollisions", testManyHashValuesIntForCollisions),
         ("testManyHashValuesString", testManyHashValuesString),
         ("testManyHashValuesStringForCollisions", testManyHashValuesStringForCollisions),
+        ("testMap", testMap),
     ]
 }
 
@@ -581,6 +589,7 @@ public func __allTests() -> [XCTestCaseEntry] {
         testCase(MutableGraphTests.__allTests),
         testCase(NewTypeTests.__allTests),
         testCase(OrderedDictionaryTests.__allTests),
+        testCase(OrderedPairTests.__allTests),
         testCase(PairsTests.__allTests),
         testCase(QueueTests.__allTests),
         testCase(ReferenceTreeProtocolTests.__allTests),