CODEWITHSUNDEEP
scalaapache-spark
user2848932
user2848932

Reputation: 786

How to Map Partial Elements in Scala/Spark

I have a list of integers: 

val mylist = List(1, 2, 3, 4)

What I want to do is to map the element which are even numbers in mylist, and multiply them by 2.

Maybe the code should be:

mylist.map{ case x%2==2 => x*2 }

I expect the result to be List(4, 8) but it's not. What is the correct code?

I know I could realize this function by using filter + map

a.filter(_%2 == 0).map(_*2)

but is there some way to realize this function by only using map()?

Upvotes: 0

Views: 679

Answers (1)

Shyamendra Solanki
Shyamendra Solanki

Reputation: 8851

map does not reduce number of elements in transformation. filter + map is right approach.

But if single method is needed, use collect:

mylist.collect{ case x if x % 2 == 0 => 2 * x }

Edit:

withFilter + map is more efficient than filter + map (as withFilter does not create intermediate collection, i.e. it works lazily):

mylist.withFilter(_ % 2 == 0).map(_ * 2)

which is same as for :

for { e <- mylist if (e % 2 == 0) } yield 2 * e

Upvotes: 3

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