# RxJava - Mathematical Operators

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Following are the operators which operates on entire items emitted by an Observable.

Sr.No. Operator & Description
1

Average

Evaluates averages of all items and emit the result.

2

Concat

Emits all items from multiple Observable without interleaving.

3

Count

Counts all items and emit the result.

4

Max

Evaluates max valued item of all items and emit the result.

5

Min

Evaluates min valued item of all items and emit the result.

6

Reduce

Apply a function on each item and return the result.

7

Sum

Evaluates sum of all items and emit the result.

## Mathematical Operator Example

Create the following Java program using any editor of your choice in, say, C:\> RxJava.

### ObservableTester.java

```import io.reactivex.Observable;
//Using concat operator to operate on multiple Observables
public class ObservableTester  {
public static void main(String[] args)  throws InterruptedException {
Integer[] numbers = { 1, 2, 3, 4, 5, 6};
String[] letters = {"a", "b", "c", "d", "e", "f", "g"};
final StringBuilder result = new StringBuilder();
Observable<String> observable1 = Observable.fromArray(letters);
Observable<Integer> observable2 = Observable.fromArray(numbers);
Observable.concat(observable1, observable2)
.subscribe( letter -> result.append(letter));
System.out.println(result);
}
}
```

### Verify the Result

Compile the class using javac compiler as follows −

```C:\RxJava>javac ObservableTester.java
```

Now run the ObservableTester as follows −

```C:\RxJava>java ObservableTester
```

It should produce the following output −

```abcdefg123456
```
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