From ea6fdbaaf2a57a9162bce2613d29f834a7c3da6d Mon Sep 17 00:00:00 2001
From: Eric Amodio <eamodio@gmail.com>
Date: Tue, 12 Sep 2017 15:47:57 -0400
Subject: [PATCH] Adds groupBy function

---
 src/system/array.ts | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/system/array.ts b/src/system/array.ts
index 8ceb1db..8a7695f 100644
--- a/src/system/array.ts
+++ b/src/system/array.ts
@@ -1,6 +1,15 @@
 'use strict';
 
 export namespace Arrays {
+    export function groupBy<T>(array: T[], accessor: (item: T) => any): T[] {
+        return array.reduce((previous, current) => {
+            const value = accessor(current);
+            previous[value] = previous[value] || [];
+            previous[value].push(current);
+            return previous;
+        }, Object.create(null));
+    }
+
     export function uniqueBy<T>(array: T[], accessor: (item: T) => any, predicate?: (item: T) => boolean): T[] {
         const uniqueValues = Object.create(null);
         return array.filter(_ => {