typescript - Array を Observable に変換し、変換を実行して、再び Array として返しますか?

Question

にngOnInit()入れたい「return x」がありObservable、変換を実行して同じ形式で再度返します。

これが作業中のプランカーです: http://plnkr.co/edit/z26799bSy17mAL4P5MiD?p=preview

import {Component} from '@angular/core'
import { Observable } from 'rxjs'
import * as Rx from 'rxjs/Rx'

@Component({
  selector: 'my-app',
  providers: [],
  template: `
    <div>
      <h2>{{name}}</h2>

      <button (click)="addToArray()">Add</button>
      <ul>
        <li *ngFor="let item of data$ | async">{{ item }}</li>
      </ul>

    </div>
  `,
  directives: []
})
export class App {

  data = ["one","two","three"]
  data$: Observable<Array<string>>;

  constructor() {
    this.name = 'Angular2 array to observable example'
  }

  ngOnInit() {
    this.data$ = Rx.Observable.of(this.data)
      .map(data => {
        let x = data
        x.push("4")

        ///
        ///  TRANSFORM X IN THIS SECTION OF THE CODE
        ///  HERE BY PUTTING IT INTO OBSERVABLE
        ///  PERFORMING TRANSFORMATIONS AND
        ///  RETURNING THE DATA TO BE RENDERED IN TEMPLATE
        ///

        return x
      })
  }

  addToArray() {
    this.data.push('more numbers')
  }      
}