filter()

The  filter() operator accepts Predicate<T> for a given Observable<T>. This means that you provide it a lambda that qualifies each emission by mapping it to a Boolean value, and emissions with false will not go forward.

For instance,  you can use filter() to only allow string emissions that are not five characters in length:

import io.reactivex.Observable;

public class Launcher {
    public static void main(String[] args) {

      Observable.just("Alpha", "Beta", "Gamma", "Delta", "Epsilon")
      .filter(s -> s.length() != 5)
      subscribe(s -> System.out.println("RECEIVED: " + s));
    }
} 

The output of the preceding code snippet is as follows:

RECEIVED: Beta
RECEIVED: Epsilon

The filter() function is probably the most commonly used operator to suppress emissions.