[RxJS] Aggregating Streams with Reduce and Scan using RxJS

What is the RxJS equivalent of the Array reduce? What if I want to emit my reduced or aggregated value @ each event? This brief tutorial covers Observable operators reduce () and scan (), their differences and gotchas.

In ES5, the Array's reduce function works like this:

var ary = [0,1,2,3,4]; var res = ary.reduce (function(PreVal, item) {  return preval+0   //ten

In RxJS, also have reduce function:

It gives the same result.

var source = Rx.Observable.fromArray ([0,1,2,3,4]); Source.reduce (function(PreVal, Item) {  return preval+0). Subscribe (function(res) {  console.clear ();  Console.log (res);});

Let's do it async:

We'll wait for 2.5 seconds until it gives result "10". This means the reduce () function in RxJS, it would not exec until the observable finihsed.

var source = Rx.Observable.interval ($). Take (5); Source.reduce (function(PreVal, Item) {  return preval+0). Subscribe (function(res) {  console.clear ();  Console.log (res);});

So if we just write:

var source = Rx.Observable.interval (500);

And never finish it, we won ' t get result by reduce () funtion.

Use SACN () function instead of the reduce () to get result for each time:

var source = Rx.Observable.interval ($). Take (5); Source.scan (function(preVal, item) {  return preval+item;}). Subscribe (function(res) {  console.log (res);}); /* 013610 */

When I run this, you'll see each time it ticks in, I get the next value, the next reduced value. One nice difference with scan though are, since it doesn ' t wait for completion, if I were to run this again, it ' s actually Going to give me a result every time.

[RxJS] Aggregating Streams with Reduce and Scan using RxJS