[ADD] partition

index.js

@@ -5,6 +5,7 @@ const foldLeft = require('./foldLeft');
 const foldRight = require('./foldRight');
 const map = require('./map');
 const partialFunction = require('./partialFunction');
+const partition = require('./partition');
 const zip = require('./zip');
 
 module.exports = {
@@ -15,5 +16,6 @@ module.exports = {
   foldRight,
   map,
   partialFunction,
+  partition,
   zip,
 };

partition/index.js

@@ -0,0 +1,12 @@
+module.exports = function partition(iterable, predicator) {
+  const left = [];
+  const right = [];
+  for (const element of iterable) {
+    if (predicator(element)) {
+      left.push(element);
+    } else {
+      right.push(element);
+    }
+  }
+  return [left, right];
+};

test/partition.test.js

@@ -0,0 +1,25 @@
+const assert = require('assert');
+const $ = require('../');
+
+describe('partition test', () => {
+  let iterable = [1, 2, 3, 4, 5, 6, 7, 8];
+  it('work with array', () => {
+    const array = Array.from(iterable);
+    const result = $.partition(array, (x) => x % 2 == 0);
+    assert.deepEqual(result, [[2, 4, 6, 8], [1, 3, 5, 7]]);
+  });
+  it('work with Set', () => {
+    const set = new Set(iterable);
+    const result = $.partition(set, (x) => x % 2 == 0);
+    assert.deepEqual(result, [[2, 4, 6, 8], [1, 3, 5, 7]]);
+  });
+  it('work with generator', () => {
+    function* oneToEight() {
+      for (let i = 1; i <= 8; i++) {
+        yield i;
+      }
+    }    
+    const result = $.partition(oneToEight(), (x) => x % 2 == 0);
+    assert.deepEqual(result, [[2, 4, 6, 8], [1, 3, 5, 7]]);
+  });
+});