Shubham Verma explains the map and flatMap functions in Scala:
Consider two sets, A = {-2, -1, 0, 1, 2} and B = {0.5, 1, 1.5, 2.5, 4, 4.5, 5, 5.5} and a function f: A => B
y = x ^ 2 + 0.5; x is an element from set A and y corresponds to an element from set B, now we see that function f is applied to every element of set A but the result could be a subset of set B also.
So from the above text, we can draw the analogy that sets A and B can be seen as any collection in programming paradigm. Now what is “f”, so “f” could be seen as a function that takes an element from A and returns an element that exists in B, the point here to note is that, as scala promotes immutability whenever we apply map (or any other transformer) on some collection of type A, it returns a new collection of the same type with elements of type B. It would be helpful to understand it from the snippet below.
val result: List[B] = List[A].map(f: A => B)So when a map operation is applied on a collection (here a List) of type A, with passing f as its argument it applies that function to every element of List of type A returns a new collection (again a List) of type B.
Read the whole thing.