Add uniqBy

README.md

@@ -141,6 +141,7 @@ objects can easily be converted to an array by use of the
 1. [_.some](#_some)
 1. [_.sortBy](#_sortby-and-_orderby)
 1. [_.uniq](#_uniq)
+1. [_.uniqBy](#_uniqBy)
 1. [_.uniqWith](#_uniqWith)
 
 **[Function](#function)**
@@ -1808,6 +1809,33 @@ Produces a duplicate-free version of the array, using === to test object equalit
 
 **[⬆ back to top](#quick-links)**
 
+### _.uniqBy
+
+Like `_.uniq` but compares the elements using the provided function or object key.
+
+  ```js
+  // Lodash: _.uniqBy
+  // Underscore: _.uniq
+  _.uniqBy([2.1, 1.2, 2.3], Math.floor);
+  // => [2.1, 1.2]
+  _.uniqBy([{ 'x': 1 }, { 'x': 2 }, { 'x': 1 }], 'x');
+  // => [{ 'x': 1 }, { 'x': 2 }]
+
+  // Native
+  [...new Map([2.1, 1.2, 2.3].map(v => [Math.floor(v), v]).reverse()).values()];
+  // => [2.1, 1.2]
+  [...new Map([{ 'x': 1 }, { 'x': 2 }, { 'x': 1 }].map(o => [o.x, o]).reverse()).values()];
+  // => [{ 'x': 1 }, { 'x': 2 }]
+  ```
+
+#### Browser Support for Spread in array literals
+
+![Chrome][chrome-image] | ![Edge][edge-image] | ![Firefox][firefox-image] | ![IE][ie-image] | ![Opera][opera-image] | ![Safari][safari-image]
+:-: | :-: | :-: | :-: | :-: | :-: |
+ 46.0  ✔  | 12.0 ✔ | 16.0 ✔ |  ✖  |  37.0 ✔  |  8.0 ✔  |
+
+**[⬆ back to top](#quick-links)**
+
 ## Function
 
 ### _.after

tests/unit/all.js

@@ -927,6 +927,21 @@ describe('code snippet example', () => {
     });
   });
 
+  describe('uniqBy', () => {
+    function uniqBy(arr, iteratee) {
+      return [...new Map(arr.map(v => [typeof iteratee === 'function' ? iteratee(v) : v[iteratee], v]).reverse()).values()];
+    };
+
+    it('should take an iteratee function', () => {
+      assert.deepStrictEqual(_.uniqBy([2.1, 1.2, 2.3], Math.floor), uniqBy([2.1, 1.2, 2.3], Math.floor));
+    });
+
+    it('should take an object key', () => {
+      assert.deepStrictEqual(_.uniqBy([{ 'x': 1 }, { 'x': 2 }, { 'x': 1 }], 'x'),
+        uniqBy([{ 'x': 1 }, { 'x': 2 }, { 'x': 1 }], 'x'));
+    });
+  });
+
   describe('capitalize', () => {
     function capitalize(string) {
       return string ? string.charAt(0).toUpperCase() + string.slice(1).toLowerCase() : '';