Get common element from 2 given lists

Question

So i have this 2 collections:

import collection.mutable.ListBuffer

val list1 = ListBuffer[(String, String)]()
list1 += (("Italy", "valid"))
list1 += (("Germany", "not valid"))
list1 += (("USA", "not valid"))
list1 += (("Romania", "valid"))

val list2 = ListBuffer[String]()
list2 += "Germany"
list2 += "USA"
list2 += "Romania"
list2 += "Italy"
list2 += "France"
list2 += "Croatia"

I want to get new list that contain common countries with specific condition for example valid so the result will be new list:

Italy, Romania

Answer 1

When you need to filter and map at the same time, use collect:

list1.collect { case (c, "valid") => c } intersect list2

Answer 2

Using a for comprehension as follows,

for ((a,"valid") <- list1 if list2.contains(a)) yield a

This comprehension desugars into a flatMap and a lazy filter. We pattern match (extract) those tuples whose second item matches "valid" and check whether the validated country belongs to the second list.