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Reactive Programming with RxJS

Reduce, Aggregate and Flatmap Operators of Sequencing

Learn to operate the reduce, aggregate and flatMap operators of sequencing.

We'll cover the following...

Reduce

The reduce operator, also known as fold, takes an Observable and returns a new one that always contains a single item, which is the result of applying a function over each element. This function receives the current element and the result of the function’s previous invocation.

Note: The reduce function has another parameter that is optional and can be used to pass a starting seed value.

var Rx = require('rx');
var src = [1,2,3,4,5];
var sum = src.reduce(function(a,b)
{
  return a+b;
});
console.log(sum);
Using the reduce operator

Now let’s run the code while subscribing to the value:

var Rx = require('rx');
var logValue = function(val) { console.log(val) };
var src = Rx.Observable.range(1, 5);
var sum = src.reduce(function(acc, x) 
{
  return acc + x;
});
sum.subscribe(logValue);
Using the reduce operator and subscribing to it

The reduce operator is a powerful operator that is used to manipulate a sequence. It is, in fact, the base implementation for a whole subset of methods called aggregate operators.

Aggregate operators

Aggregate operators process a sequence and return a single value. For example, Rx.Observable.first takes an Observable and an optional predicate function and returns the first element that satisfies the condition in the ...