Reactive JS (RxJs) Group by key

Question

I have a data stream with e.g. the following values:

Observable.of(
    [{time: 1000, a: 100},
    {time: 1000, b: 100},
    {time: 2000, a: 200}]
);

And need to merge the values based on time to get:

[{time: 1000, a: 100, b: 100},
{time: 2000, a: 200}]

I can use map and reduce but then I end up with a single map that I have to split somehow again. Is there a more straight forward way in RxJs?

Answer 1

You could just do an array reduce inside of a map operator. Might be a bit clearer than the groupBy and flatMap. This is more of a data mapping issue than an rxjs issue.

Rx.Observable.of(
	[{time: 1000, a: 100},
   {time: 1000, b: 100},
   {time: 2000, a: 200}]
).map(data => {
  return data.reduce((acc, cur) => {
    const index = acc.findIndex(x => x.time === cur.time);
    if (index >= 0) {
      acc[index] = { ...acc[index], ...cur };
    } else {
      acc.push(cur);
    }
    return acc;
  }, [])
})
.subscribe(x => { console.log('result', x); });

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