From 997f44f9f69d8917e0e1165db3eb9652d2b73bc1 Mon Sep 17 00:00:00 2001
From: HelloRusk <36184621+7ma7X@users.noreply.github.com>
Date: Wed, 6 Mar 2019 10:17:31 +0900
Subject: [PATCH] implement Map and Reduce (#5)

---
 readme.md     | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++
 src/index.js  | 17 ++++++++++++++
 test/index.js | 26 +++++++++++++++++++++
 3 files changed, 105 insertions(+)

diff --git a/readme.md b/readme.md
index 7323740..07b715c 100755
--- a/readme.md
+++ b/readme.md
@@ -28,7 +28,9 @@ ECMAScript 6 sets have no methods for computing the union (∪), intersection (
 - **⊖** symmetric difference
 - **⊆** subset
 - **⊇** superset
+- map
 - filter
+- reduce
 
 
 ## Install
@@ -152,6 +154,21 @@ Type: `Zet|Set`
 
 Set of type `Zet` or `Set`.
 
+### map(set, func)
+Returns: `Zet|Set`
+
+Creates a set with the results of calling the provided function on every element.
+
+#### set
+Type: `Zet|Set`
+
+Set of type `Zet` or `Set`.
+
+#### func
+Type: `Function`
+
+Function that produces an element of the new set.
+
 ### filter(set, func)
 Returns: `Zet|Set`
 
@@ -166,6 +183,26 @@ Type: `Function`
 
 It is a predicate, to test each element of the set.
 
+### reduce(set, func, *initializer*)
+Returns: `Number`
+
+Reduces the set to a single value, by executing the provided function for each element in the set (from left-to-right).
+
+#### set
+Type: `Zet|Set`
+
+Set of type `Zet` or `Set`.
+
+#### func
+Type: `Function`
+
+Function to be executed for each element in the set.
+
+#### *initializer*
+Type: `Number`
+
+Optional. A value to be passed to the function as the initial value.
+
 ## Instance Methods
 
 ### union(...sets) ∪
@@ -228,6 +265,16 @@ Type: `Zet|Set`
 
 Set of type `Zet` or `Set`.
 
+### map(func)
+Returns: `Zet|Set`
+
+Creates a set with the results of calling the provided function on every element.
+
+#### func
+Type: `Function`
+
+Function that produces an element of the new set.
+
 ### filter(func)
 Returns: `Zet|Set`
 
@@ -238,6 +285,21 @@ Type: `Function`
 
 It is a predicate, to test each element of the set.
 
+### reduce(func, *initializer*)
+Returns: `Number`
+
+Reduces the set to a single value, by executing the provided function for each element in the set (from left-to-right).
+
+#### func
+Type: `Function`
+
+Function to be executed for each element in the set.
+
+#### *initializer*
+Type: `Number`
+
+Optional. A value to be passed to the function as the initial value.
+
 ## License
 
 MIT © [Terkel Gjervig](https://terkel.com)
diff --git a/src/index.js b/src/index.js
index 8b534df..788d2a4 100644
--- a/src/index.js
+++ b/src/index.js
@@ -26,10 +26,19 @@ class Zet extends Set {
     return [...setB].every(x => setA.has(x));
   }
 
+  static map(set, func) {
+    return new Zet([...set].map(func));
+  }
+
   static filter(set, func) {
     return new Zet([...set].filter(func));
   }
 
+  static reduce(set, func, initializer) {
+    if (initializer === undefined) return [...set].reduce(func);
+    return [...set].reduce(func, initializer);
+  }
+
   union(...sets) {
     return Zet.union(this, ...sets);
   }
@@ -54,9 +63,17 @@ class Zet extends Set {
     return Zet.superset(this, other);
   }
 
+  map(func) {
+    return Zet.map(this, func);
+  }
+
   filter(func) {
     return Zet.filter(this, func);
   }
+
+  reduce(func, initializer) {
+    return Zet.reduce(this, func, initializer);
+  }
 }
 
 export default Zet;
diff --git a/test/index.js b/test/index.js
index 1541123..f69786c 100755
--- a/test/index.js
+++ b/test/index.js
@@ -81,12 +81,25 @@ test('static :: superset ⊇', t => {
   t.end();
 });
 
+test('static :: map', t => {
+  let x = new Zet([1,4,9,16]);
+  eq(t, Zet.map(x, i => i * 2), [2,8,18,32]);
+  t.end();
+});
+
 test('static :: filter', t => {
   let x = new Zet([1,2,3]);
   eq(t, Zet.filter(x, i => i % 2), [1, 3]);
   t.end();
 });
 
+test('static :: reduce', t => {
+  let x = new Zet([1,2,3,4]);
+  t.is(Zet.reduce(x, (i, j) => i + j), 10);
+  t.is(Zet.reduce(x, (i, j) => i + j, 5), 15);
+  t.end();
+});
+
 test('instance :: union ∩', t => {
   let x = new Zet([1,2,3]);
   let y = new Zet([2,3,4]);
@@ -150,8 +163,21 @@ test('instance :: superset ⊇', t => {
   t.end();
 });
 
+test('instance :: map', t => {
+  let x = new Zet([1,4,9,16]);
+  eq(t, x.map(i => i * 2), [2,8,18,32]);
+  t.end();
+});
+
 test('instance :: filter', t => {
   let x = new Zet([1,2,3]);
   eq(t, x.filter(i => i % 2), [1, 3]);
   t.end();
 });
+
+test('instance :: reduce', t => {
+  let x = new Zet([1,2,3,4]);
+  t.is(x.reduce((i, j) => i + j), 10);
+  t.is(x.reduce((i, j) => i + j, 5), 15);
+  t.end();
+});