Scala find element in nested List

Question

Consider the following example:

case class Person(name: String, age: Int)
case class Family(surname: String, members: List[Person])

val families = List(
  Family("Jones",
    List(Person("Indiana", 50), Person("Molly", 20))),
  Family("Black",
    List(Person("Jack", 55), Person("Derek", 12))))

I want to write a function that finds a person with a certain name in a List[Family] object. This is my current solution:

def find(name: String, families: List[Family]): Option[Person] = {
  families.find(f => f.members.exists(m => m.name == name)).map(f => f.members.find(m => m.name == name).get)
}

Is there a more efficient and elegant (and functional) way to achieve this?

families.flatMap(_.members).find(_.name == name) does the job. But your data model appears badly chosen, because there is no way to get the surname of Person. — ziggystar
– ziggystar, Commented Jan 28, 2016 at 15:20
@ziggystar depends on how you want to process it, see my answer below — Victor Moroz
– Victor Moroz, Commented Jan 28, 2016 at 18:00

Jean Logeart · Accepted Answer · 2016-01-28 15:19:54Z

7

You can try:

families.flatMap(_.members).find(_.name == name)

answered Jan 28, 2016 at 15:19

Jean Logeart

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1 Comment

bashan Over a year ago

Assuming you want to find only the first match, isn't it less efficient?

elm · Accepted Answer · 2016-01-28 19:59:43Z

2

Using a for comprehension like this,

for (f <- families; m <- f.members if m.name == name) yield m

Namely for each family member pick those whose name is as desired.

answered Jan 28, 2016 at 19:59

elm

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Comments

Andrew Whitaker · Accepted Answer · 2016-01-28 15:19:30Z

1

You could just use flatMap and find:

families.flatMap(fam => fam.members).find(m => m.name == name)

answered Jan 28, 2016 at 15:19

Andrew Whitaker

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Comments

Victor Moroz · Accepted Answer · 2016-01-28 17:58:53Z

0

Functionally I would prefer this way (added surname too, you probably need it, it makes it a bit more complicated):

families.flatMap { f => f.members
                         .find(_.name == "Molly")
                         .map { m => (f.surname, m.name) }}
        .headOption
//> res0: Option[(String, String)] = Some((Jones,Molly))

and if you want all people with the given name, just replace .find with .filter and remove .headOption

answered Jan 28, 2016 at 17:58

Victor Moroz

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Comments

Joe Stogner · Accepted Answer · 2018-01-02 21:53:55Z

0

if you wanted to find just the family.

families.find(f => f.members.exists(_.name == name))

answered Jan 2, 2018 at 21:53

Joe Stogner

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