Scala | flatMap Method

In Scala, flatMap() method is identical to the map() method, but the only difference is that in flatMap the inner grouping of an item is removed and a sequence is generated. It can be defined as a blend of map method and flatten method. The output obtained by running the map method followed by the flatten method is same as obtained by the flatMap(). So, we can say that flatMap first runs the map method and then the flatten method to generate the desired result. Note:

• It has a built-in Option class as an Option can be expressed as a sequence which has at most one element i.e, either its empty or has only one element.
• The flatten() method is utilized to disintegrate the elements of a Scala collection in order to construct a single collection with the elements of similar type.

Let's see an example to illustrate, how the flatMap is working.

val name = Seq("Nidhi", "Singh")

Case 1: let's apply map() and flatten() on the stated sequence.

// Applying map() val result1 = name.map(_.toLowerCase) // Output List(nidhi, singh) // Applying flatten() now, val result2 = result1.flatten // Output List(n, i, d, h, i, s, i, n, g, h)

Case 2: let's apply flatMap() directly on the given sequence.

name.flatMap(_.toLowerCase)
 
// Output
List(n, i, d, h, i, s, i, n, g, h)

So, we can see here that the output obtained in both the cases is same therefore, we can say that flatMap is a combination of map and flatten method. Now, let's see some examples of flatMap method.

• Utilizing flatMap on a sequence of Strings. Example:
  Output:

  List(G, E, E, K, S, F, O, R, G, E, E, K, S)
  

  Here, flatMap is applied to the stated sequence so, a list of sequence of characters is generated.
• Applying flatMap with another functions. Example :
  Output:

  List(1, 2, 3, 2, 3, 4, 3, 4, 5)
  

  Here, flatMap is applied on the another function defined in the program and so a list of sequence of numbers is generated. Let's see how the output is computed.

  List(List(2-1, 2, 2+1), List(3-1, 3, 3+1), List(4-1, 4, 4+1))
  
  // After evaluation we get,
  List(List(1, 2, 3), List(2, 3, 4), List(3, 4, 5))
  

  So, first step works like applying map method on the another function stated.

  List(1, 2, 3, 2, 3, 4, 3, 4, 5)
  

  The second step works like applying flatten to the output obtained by the map method at the first step. Example :
  Output:

  List(4, 3, 5, 4, 6, 5, 7, 6)
  

  Here, also output is obtained like the first example of the flatMap with another functions.
• Utilizing flatMap on if-else statements. Example :
  Output:

  List(-8, 15, -22, -23, 24)
  

  Here, if an element of the sequence given satisfies the stated condition then that element is returned else negative of that element is obtained.