Flatmap

flatMap is map then flatten

flatten requires that each element is traversable

flatMap has something to do with burrito

Table of contents...

flatten

Flatten reduces one level of any Traversable

List(List(1),List(2),List(3))
	.flatten //List(1, 2, 3) (result)

Option is Traversable with 0 or 1 elements

Some("A").size //1 (result)

None.size //0 (result)

List(Some(1),Some(2),Some(3))
	.flatten //List(1, 2, 3) (result)

Flatten can be applied to any Traversable

List(Map(1->3),Map(1->8),Map(5->"A"))
	.flatten //List((1,3), (1,8), (5,A)) (result)

flatten can be applied to Nil

Nil.flatten //List() (result)

flatten and map

define items...

val items = List(List("X"),List(2),List(3))

items //List(List(X), List(2), List(3)) (result)

typeOf(items) //List[List[Any]] (result)

and function foo. Function must return a traversable

def foo(x : List[Any]) : List[String]= List("foo(" + x + ")")

apply map to each item

val mapitems = items.map(foo)

mapitems

Output

List(List(foo(List(X))), List(foo(List(2))), List(foo(List(3))))

typeOf(mapitems) //List[List[String]] (result)

apply flatten to the result of map

val flatmapitems = mapitems.flatten

flatmapitems

Output

List(foo(List(X)), foo(List(2)), foo(List(3)))

typeOf(flatmapitems) //List[String] (result)

flatMap

flatMap is map then flatten...

val flatmapitems2 = items.flatMap(foo)

flatmapitems2

Output

List(foo(List(X)), foo(List(2)), foo(List(3)))

typeOf(flatmapitems2) //List[String] (result)

flatMap usecases

join few lists...