Merge pull request #25 from silvermine/jrthomer/pluck

feat: pluck

Author: jthomerson

src/index.ts

@@ -22,4 +22,5 @@ export * from './utils/is-undefined';
 
 export * from './utils/chunk';
 export * from './utils/flatten';
+export * from './utils/pluck';
 export * from './utils/delay';

src/utils/pluck.ts

@@ -0,0 +1,5 @@
+export function pluck<T, K extends keyof T>(sources: T[], key: K): T[K][] {
+   return sources.map((o) => {
+      return o[key];
+   });
+}

tests/utils/pluck.test.ts

@@ -0,0 +1,45 @@
+import { expect } from 'chai';
+import { pluck } from '../../src';
+
+interface Location {
+   city: string;
+   state: string;
+}
+
+interface Person {
+   firstName: string;
+   middleInitial?: string;
+   lastName: string;
+   age: number;
+   location?: Location;
+}
+
+const PEOPLE: Person[] = [
+   { firstName: 'John', lastName: 'Doe', age: 21 },
+   { firstName: 'Jane', lastName: 'Doe', age: 22, location: { city: 'New York', state: 'NY' } },
+   { firstName: 'Wile', middleInitial: 'E', lastName: 'Coyote', age: 12, location: { city: 'Tucson', state: 'AZ' } },
+   { firstName: 'Road', lastName: 'Runner', age: 12, location: { city: 'Tucson', state: 'AZ' } },
+];
+
+describe('pluck', () => {
+
+   it('works correctly', () => {
+      // Explicitly type the results so we can make sure that our types on pluck are
+      // implemented correctly.
+      const firstNames: string[] = pluck(PEOPLE, 'firstName'),
+            ages: number[] = pluck(PEOPLE, 'age'),
+            middleInitials: (string | undefined)[] = pluck(PEOPLE, 'middleInitial'),
+            locations: (Location | undefined)[] = pluck(PEOPLE, 'location');
+
+      expect(firstNames).to.eql([ 'John', 'Jane', 'Wile', 'Road' ]);
+      expect(ages).to.eql([ 21, 22, 12, 12 ]);
+      expect(middleInitials).to.eql([ undefined, undefined, 'E', undefined ]);
+      expect(locations).to.eql([
+         undefined,
+         { city: 'New York', state: 'NY' },
+         { city: 'Tucson', state: 'AZ' },
+         { city: 'Tucson', state: 'AZ' },
+      ]);
+   });
+
+});