在Angular 2+中，条件观察映射是一种常见的模式，它可以根据某些条件从一个Observable流中动态地选择不同的流。这可以通过使用rxjs中的一些操作符来实现，如switchMap、mergeMap、concatMap等。

下面是一个示例代码，在这个示例中，我们从一个http请求的observable流中获取用户数据，然后根据他们的年龄从不同的数据流中获取他们的就业数据。

import { Observable, of } from 'rxjs';
import { map, switchMap } from 'rxjs/operators';
import { HttpClient } from '@angular/common/http';

interface User {
  id: number;
  name: string;
  age: number;
}

interface Employment {
  id: number;
  userId: number;
  company: string;
  salary: number;
}

@Component({
  selector: 'app-user-employment',
  templateUrl: './user-employment.component.html',
  styleUrls: ['./user-employment.component.scss']
})
export class UserEmploymentComponent implements OnInit {
  users$: Observable;
  employments$: Observable;

  constructor(private httpClient: HttpClient) { }

  ngOnInit() {
    this.users$ = this.httpClient.get('/users');

    this.employments$ = this.users$.pipe(
      switchMap(users => {
        const youngUsers$ = of(users.filter(user => user.age < 25));
        const midAgeUsers$ = of(users.filter(user => user.age >= 25 && user.age <= 45));
        const oldUsers$ = of(users.filter(user => user.age > 45));

        return youngUsers$.pipe(map(() => this.httpClient.get('/youngUsersEmployments')))
          .pipe(switchMap(s => s), map((emps: any) => emps.result))
          .pipe(concat(midAgeUsers$.pipe(map(() => this.httpClient.get('/middleAgedUsersEmployments')))
            .pipe(switchMap(s => s), map((emps: any) => emps.result))))
          .pipe(concat(oldUsers$.pipe(map(() => this.httpClient.get('/oldUsersEmploy