Add definitions for _(...).groupBy

lodash/lodash-tests.ts

@@ -380,6 +380,10 @@ result = <_.Dictionary<number[]>>_.groupBy([4.2, 6.1, 6.4], function(num) { retu
 result = <_.Dictionary<number[]>>_.groupBy([4.2, 6.1, 6.4], function(num) { return this.floor(num); }, Math);
 result = <_.Dictionary<string[]>>_.groupBy(['one', 'two', 'three'], 'length');
 
+	result = <_.LoDashObjectWrapper<_.Dictionary<number[]>>>_([4.2, 6.1, 6.4]).groupBy(function(num) { return Math.floor(num); });
+	result = <_.LoDashObjectWrapper<_.Dictionary<number[]>>>_([4.2, 6.1, 6.4]).groupBy(function(num) { return this.floor(num); }, Math);
+	result = <_.LoDashObjectWrapper<_.Dictionary<string[]>>>_(['one', 'two', 'three']).groupBy('length');
+
 result = <_.Dictionary<IKey>>_.indexBy(keys, 'dir');
 result = <_.Dictionary<IKey>>_.indexBy(keys, function(key) { return String.fromCharCode(key.code); });
 result = <_.Dictionary<IKey>>_.indexBy(keys, function(key) { this.fromCharCode(key.code); }, String);

lodash/lodash.d.ts

@@ -1761,6 +1761,27 @@ declare module _ {
 			whereValue: W): Dictionary<T[]>;
 	}
 
+	interface LoDashArrayWrapper {
+		/**
+		* @see _.groupBy
+		**/
+		groupBy<T>(
+			callback: ListIterator<T, any>,
+			thisArg?: any): _.LoDashObjectWrapper<Dictionary<T[]>>;
+
+		/**
+		* @see _.groupBy
+		**/
+		groupBy<T>(
+			pluckValue: string): _.LoDashObjectWrapper<Dictionary<T[]>>;
+
+		/**
+		* @see _.groupBy
+		**/
+		groupBy<W, T extends W>(
+			whereValue: W): _.LoDashObjectWrapper<Dictionary<T[]>>;
+	}
+
 	//_.indexBy
 	interface LoDashStatic {
 		/**