filter selects all the elements that satisfy a specific predicate. It can be defined formally as follows:

def filter(p: (A) ⇒ Boolean): Traversable[A]  

Let's see an example as follows:

scala> //Given a list of tuples (cities, Populations)
scala> // Get all cities that has population more than 5 million
scala> List(("Dublin", 2), ("NY", 8), ("London", 8)) filter (x =>x._2 >= 5)
res3: List[(String, Int)] = List((NY,8), (London,8))

A map is used to build a new collection or set of elements by traversing a function to all elements of the collection. In the next subsection, we will see an example of using Map.