You will likely have moments when you need to take a series of emitted values and aggregate them into a single value (usually emitted through a Single). We will cover a few operators that accomplish this. Note that nearly all of these operators only work on a finite Observable that calls onComplete() because, typically, we can aggregate only finite datasets. We will explore this behavior as we cover these operators.
Reducing operators
count()
The count() operator counts the number of emitted items and emits the result through a Single once onComplete() is called. Here is an example:
import io.reactivex.rxjava3.core.Observable;
public class Ch3_22 {
public static void main(String[] args) {
Observable.just("Alpha...