Map vs FlatMap in Kotlin?

Answer

These are transformation operators for collections and flows.

map

• Function: Transforms each element T into R.
• Result: Returns a list of the transformed items.
• Example: [1, 2, 3].map { it * 2 } -> [2, 4, 6]

flatMap

• Function: Transforms each element T into an Iterable/List of R, and then flattens all the lists into a single list.
• Result: Returns a single flattened list.
• Example:

  Copy codeval users = listOf(User("A", listOf("Order1")), User("B", listOf("Order2")))
  
  // map returns List<List<String>>
  users.map { it.orders } -> [[Order1], [Order2]]
  
  // flatMap returns List<String>
  users.flatMap { it.orders } -> [Order1, Order2]