I was just reading Daniel Spiewak's blog regading the use of Scala's flatmap operation. It seems to be one of those confusing parts of Scala so I thought I'd post a clear example of how and why you'd want to use a flatmap on a list of things.

import junit.framework.TestCase

import scala.collection.mutable.ListBuffer



class Person {



  val pets = new ListBuffer[String]()

}



class ScalaTest extends TestCase {



  def testFlatMap() {



    // let's create some people, add some pets to them

    // the end result is we went to know all the pet's that these people have

    val p = new Person;

    p.pets += "cat"

    p.pets += "dog"



    val d = new Person;

    d.pets += "fish"

    d.pets += "bird"

    d.pets += "dog"



    val people = p :: d :: Nil



    val pets = people.flatMap(_.pets)



    // show me all the pets that we have in our people collection

    println(pets) // List(cat, dog, fish, bird, dog)



    // get just the unique pets that everyone has

    println(pets.toSet)  // Set(cat, dog, fish, bird)



  }



}