map and flatmap

Question

What is the difference between map() and flatmap()?

Answer 1

The map() transformation takes in a function and applies it to each element in the RDD with the result of the function being the new value of each element in the resulting RDD. Sometimes we want to produce multiple output elements for each input element. The operation to do this is called flatMap(). As with map(), the function we provide to flatMap() is called individually for each element in our input RDD. Instead of returning a single element, we return an iterator with our return values.

Answer 2

map(): Return a new distributed dataset formed by passing each element of the source through the function 

Example: 

val a = sc . parallelize ( List (" dog " , " salmon " , " salmon " , " rat " , " elephant") , 3)

val b = a . map ( _ . length )

val c = a . zip ( b )

c . collect

flatmap(): Similar to map, but allows emitting more than one item in the map function​

Example:

val a = sc . parallelize (1 to 10 , 5)

a . flatMap (1 to _ ) . collect