feat(PickPipe): Add pick pipe

README.md

@@ -48,6 +48,7 @@
     - [keys](#keys)
     - [values](#values)
     - [pairs](#pairs)
+    - [pick](#pick)
  - [Math](#math)   
     - [min](#min)
     - [max](#max)
@@ -279,7 +280,6 @@ API: `string | underscore`
 <p>{{'FooBar' | underscore }}</p> <!-- Output: "foo_bar" -->
 ```
 
-
 ## Array
 
 ### diff
@@ -579,6 +579,17 @@ API: `object | pairs`
 <p>{{ {foo: [1, 2], bar: [3, 4]} | pairs }}</p> <!-- Output: "[['foo', [1, 2]], ['bar', [3, 4]]]" -->
 ```
 
+### pick
+
+Returns object with picked keys from object
+
+API: `object | pick: [key | string]]`
+
+```html
+<p>{{ {foo: 1, bar: 2} | pick: 'foo' }}</p> <!-- Output: "{foo: 1}" -->
+<p>{{ {foo: 1, bar: 2} | pick: 'foo': 'bar' }}</p> <!-- Output: "{foo: 1, bar: 2}" -->
+```
+
 ## Math
 
 ### min

src/app/pipes/object/index.ts

@@ -1,19 +1,21 @@
 import { KeysPipe } from './keys';
 import { ValuesPipe } from './values';
 import { PairsPipe } from './pairs';
+import { PickPipe } from './pick';
 import { NgModule } from '@angular/core';
 
 const OBJECT_PIPES = [
-  KeysPipe, ValuesPipe, PairsPipe
+  KeysPipe, ValuesPipe, PairsPipe, PickPipe
 ];
 
 @NgModule({
-  declarations: [ ...OBJECT_PIPES ],
+  declarations: OBJECT_PIPES,
   imports: [],
-  exports: [ ...OBJECT_PIPES ]
+  exports: OBJECT_PIPES
 })
 export class NgObjectPipesModule {}
 
 export * from './keys';
 export * from './values';
 export * from './pairs';
+export * from './pick';

src/app/pipes/object/pick.spec.ts

@@ -0,0 +1,26 @@
+import {PickPipe} from './pick';
+
+describe('PickPipe', () => {
+  let pipe: PickPipe;
+
+  beforeEach(() => {
+    pipe = new PickPipe();
+  });
+
+  it('should keep the element the same way if its not an object', () => {
+    expect(pipe.transform([1, 2, 3])).toEqual([1, 2, 3]);
+    expect(pipe.transform([])).toEqual([]);
+    expect(pipe.transform('foo')).toEqual('foo');
+    expect(pipe.transform(null)).toEqual(null);
+    expect(pipe.transform(undefined)).toEqual(undefined);
+  });
+
+  it('should return picked object by args', () => {
+    expect(pipe.transform({})).toEqual({});
+    expect(pipe.transform({foo: 1})).toEqual({});
+    expect(pipe.transform({a: 1, b: 2, c: 3}, 'a')).toEqual({a: 1});
+    expect(pipe.transform({a: 1, b: 2, c: 3}, 'a', 'b')).toEqual({a: 1, b: 2});
+    expect(pipe.transform({a: 1, b: 2, c: 3}, 'b', 'c')).toEqual({b: 2, c: 3});
+    expect(pipe.transform({a: 1, b: 2, c: 3}, 'b')).toEqual({b: 2});
+  });
+});

src/app/pipes/object/pick.ts

@@ -0,0 +1,16 @@
+import {PipeTransform, Pipe} from '@angular/core';
+import GeneralHelper from '../helpers/helpers';
+
+@Pipe({name: 'pick'})
+export class PickPipe implements PipeTransform {
+
+  transform(obj: any, ...args: Array<string>): Object {
+    if (Array.isArray(obj) || !GeneralHelper.isObject(obj)) {
+      return obj;
+    }
+
+    return Object.keys(obj)
+      .filter(k => !!~args.indexOf(k))
+      .reduce((o, k) => Object.assign(o, {[k]: obj[k]}), {});
+  }
+}