var projection = ["a", "b", "c"];
var count = 0;
Rx.Observable.range(1, 3)
  .do(Rx.Observer.create(
    x  => console.log(`Generate Next ${x}`),
    e  => console.log(`Generate Error ${e.message}`),
    () => console.log(`Generate Completed`)
  ))
  .manySelect(ys => {
    var k = ++count;
    return ys.map(x => `${k}, ${projection[x - 1]}`);
  })
  .mergeAll()
  .subscribe(Rx.Observer.create(
    x  => console.log(`Next ${x}`),
    e  => console.log(`Error ${e.message}`),
    () => console.log(`Completed`)
  ));