3.4 Added switchMap

Author: Froussios

Part 3 - Taming the sequence/4. Combining sequences.md

@@ -429,7 +429,7 @@ Observable.switchOnNext(
 				.map(i2 -> i)
 		)
 	)
-	.take(10)
+	.take(9)
 	.subscribe(System.out::println);
 ```
 Outpu
@@ -443,11 +443,42 @@ Outpu
 2
 2
 2
-3
 ```
 
 This example may be a bit confusing. What we've done is create an observable that creates a new observable every 100ms. Every created observable emits it's number in the sequence every 30ms.
 
+#### switchMap
+
+Where `flatMap` internally uses `merge` to combine the generated sequences, there is `switchMap` to use `switchOnNext` in place of `merge`.
+
+```java
+public final <R> Observable<R> switchMap(Func1<? super T,? extends Observable<? extends R>> func)
+```
+![](https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/switchMap.png)
+
+Every value from the source observable is mapped through `func` to an observable. The values from the generated observable are emitted by the returned observable. Every time a new value arrives, `func` generates a new observable and switches to it, dropping the old one. The example we showed for `switchOnNext` can also be implemented with `switchMap`:
+
+```java
+Observable.interval(100, TimeUnit.MILLISECONDS)
+	.switchMap(i -> 
+		Observable.interval(30, TimeUnit.MILLISECONDS)
+			.map(l -> i))
+	.take(9)
+	.subscribe(System.out::println);
+```
+Output
+```
+0
+0
+0
+1
+1
+1
+2
+2
+2
+```
+
 
 ## Pairing sequences