如何在Angular 2中清除“distinct”RxJS运算符？

import { Component } from '@angular/core';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/distinctUntilChanged';

@Component({
  selector: 'app-example',
  template: `
    <div>
      <h2>Distinct Example</h2>
      <ul>
        <li *ngFor="let item of items$ | async">{{ item }}</li>
      </ul>
    </div>
  `,
})
export class ExampleComponent {
  items$: Observable<number>;

  constructor() {
    this.items$ = Observable.of(1, 1, 2, 2, 3, 3, 4, 4)
      .distinctUntilChanged();
  }
}