[RxJS] Split an RxJS Observable into groups with groupBy

groupBy() is another RxJS operator to create higher order observables. In this lesson we will learn how groupBy works for routing source values into different groups according to a calculated key.

const numbersObservable = Rx.Observable.interval(500).take(5);

numbersObservable
  .groupBy(x => x % 2)
  .map(innerObs => innerObs.count())
  .mergeAll()
  .subscribe(x => console.log(x));

/*
--0--1--2--3--4|

 groupBy(x => x % 2)

--+--+---------|
  \    \  1-----3---|
  0-----2-----4|

 map(innerObs => innerObs.count())

--+--+---------|
  \    \  ---------2|
  ------------3|

 mergeAll

--------------(3,2)|

*/