Kotlin - filtering a list of objects by comparing to a list of properties

Question

I have a class Person:

class Person(var fullName: String, var nickname: String, var age: Int)

In my code, at some point I have a List of Person objects, and a list of nicknames.

var people: List<Person> = listOf(
  Person("Adam Asshat", "dontinviteme", 21),
  Person("Bob Bowyer", "bob", 37),
  Person("Emily Eden", "emily", 22)
)

var invitedToParty: List<String> = listOf("bob", "emily")

Now I want to get a List with only Bob and Emily by using lambda's, but I'm not sure how I'd go about it in Kotlin.

var invitedPeople: List<Person> = // a lambda that results in a list containing only Bob and Emily's objects

In C# I'd probably use LINQ and a .where()-method combined with an == any() but Kotlin doesn't seem to have anything like that from what I've found.

Is this even possible in Kotlin lambda's?

Solution 1

In C# you'd do:

people.Where(p => invitedToParty.Any(s => s == p.nickname));

Likewise in Kotlin, you'd use filter which is like Where and any speaks for it self:

people.filter { p -> invitedToParty.any { it == p.nickname } }

or using contains:

people.filter { invitedToParty.contains(it.nickname) }

Solution 2

You can use the .filter() function to do this:

val invitedPeople: List<Person> = people.filter { it.nickname == "bob" || it.nickname == "emily" }

Or you can do this set-based:

val invitedPeople: List<Person> = people.filter { it.nickname in setOf("bob", "emily") }

Comments

[Joffrey]

Why not simply people.filter { invitedToParty.contains(it.nickname) }?

[Ousmane D.]

@Joffrey I guess one could do that as well. updated to accommodate your comment.

[Joffrey]

Thanks, in fact, I just realized there is more idiomatic in kotlin with the in operator: people.filter { it.nickname in invitedToParty }

[Ousmane D.]

@Joffrey agreed, there are definitely several ways to go about this, I just thought I'd show the filter + any approach since that is the one OP is familiar with in C#. nevertheless, it's good to be suggested better solutions indeed. thanks!

[The Fox]

Thanks for your suggestions, Aomine and Joffrey. I'm always happy to learn multiple ways to accomplish something, I'll be trying this out as soon as I get back to my home laptop and then accept your answer.

[The Fox]

Set-based seems most appropriate for my purposes; your first approach is hard-coded, which isn't what I need for my actual problem. Thank you

[Blundell]

any is the most flexible when it as the main object is not what you need but a parameter of it i.e. it.nickname == p.nickname