Scala - convert a list to a HashMap based on list member variable values

Question

I have an object, A that contains another object, B. B contains two strings, stringOne and stringTwo.

Given that I have a list / sequence of A's,

Is it possible to create a map from the list of A's, that results in a HashMap of type A -> Seq[B], where what goes into Seq[B] are B items with identical B.stringOne and B.stringTwo?

A and B are case classes.

It is usually better to demonstrate the problem, with code, rather than trying to describe the problem, with words. — jwvh
– jwvh, Commented Sep 15, 2016 at 0:03
If you have list of tuples e.g a->10, b->20, c->30 then You can transform that to a map by applying myList.to(ListMap) — hartmut27
– hartmut27, Commented Jun 1, 2022 at 19:37

Samar · Accepted Answer · 2016-09-15 01:13:30Z

1

Are you looking for something like this:

case class B(s1: String, s2: String) 
case class A(b: B) 
val ls = List( A(B("1","2")), A(B("3","4")), A(B("5","6")),  A(B("1","2")))
ls.groupBy(identity).map({case (k,v) => (k, v.map(_.b))})

//Output: Map(A(B(1,2)) -> List(B(1,2), B(1,2)), A(B(3,4)) -> List(B(3,4)), A(B(5,6)) -> List(B(5,6)))

answered Sep 15, 2016 at 1:13

Samar

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