From 39d15d6087724bcd0c8d87f48edfb945b96bc3d8 Mon Sep 17 00:00:00 2001
From: Jason Rudolph & Nathan Sobo <jasonrudolph+nathan@github.com>
Date: Wed, 31 Jul 2013 16:21:41 -0700
Subject: [PATCH] Add _.isSubset

---
 spec/stdlib/underscore-extensions-spec.coffee | 8 ++++++++
 src/stdlib/underscore-extensions.coffee       | 3 +++
 2 files changed, 11 insertions(+)

diff --git a/spec/stdlib/underscore-extensions-spec.coffee b/spec/stdlib/underscore-extensions-spec.coffee
index 7bf4bf90d..f75a720d8 100644
--- a/spec/stdlib/underscore-extensions-spec.coffee
+++ b/spec/stdlib/underscore-extensions-spec.coffee
@@ -107,3 +107,11 @@ describe "underscore extensions", ->
           object:
             first: 1
             second: 2
+
+  describe "_.isSubset(potentialSubset, potentialSuperset)", ->
+    it "returns whether the first argument is a subset of the second", ->
+      expect(_.isSubset([1, 2], [1, 2])).toBeTruthy()
+      expect(_.isSubset([1, 2], [1, 2, 3])).toBeTruthy()
+      expect(_.isSubset([], [1])).toBeTruthy()
+      expect(_.isSubset([], [])).toBeTruthy()
+      expect(_.isSubset([1, 2], [2, 3])).toBeFalsy()
diff --git a/src/stdlib/underscore-extensions.coffee b/src/stdlib/underscore-extensions.coffee
index 7d203ce76..5ad04b67a 100644
--- a/src/stdlib/underscore-extensions.coffee
+++ b/src/stdlib/underscore-extensions.coffee
@@ -195,4 +195,7 @@ _.mixin
       newObject[key] = value if value?
     newObject
 
+  isSubset: (potentialSubset, potentialSuperset) ->
+    _.every potentialSubset, (element) -> _.include(potentialSuperset, element)
+
 _.isEqual = require 'tantamount'