groupby.md

groupBy

signature: groupBy(keySelector: Function, elementSelector: Function): Observable

Group into observables based on provided value.

Examples

Example 1: Group by property

( jsBin | jsFiddle )

const people = [
  { name: 'Sue', age: 25 },
  { name: 'Joe', age: 30 },
  { name: 'Frank', age: 25 },
  { name: 'Sarah', age: 35 }
];
//emit each person
const source = Rx.Observable.from(people);
//group by age
const example = source
  .groupBy(person => person.age)
  // return each item in group as array
  .mergeMap(group => group.toArray());
/*
  output:
  [{age: 25, name: "Sue"},{age: 25, name: "Frank"}]
  [{age: 30, name: "Joe"}]
  [{age: 35, name: "Sarah"}]
*/
const subscribe = example.subscribe(val => console.log(val));

Additional Resources

• groupBy 📰 - Official docs
• Group higher order observables with RxJS groupBy 📹 💵 - André Staltz
• Use groupBy in real RxJS applications 📹 💵 - André Staltz

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📁 Source Code: https://github.com/ReactiveX/rxjs/blob/master/src/operator/groupBy.ts