Hi All, I have a `Iterable<A>` and want to c...

# announcements

[Xuc Xiem]

Hi All, I have a Iterable<A> and want to create a Map<A, Int> with a function f: A -> Int?. The values in the map cannot be null. So I write something like this:

iterable
  .map { Pair(it, f(it)) }      // Iterable<Pair<A, Int?>>
  .filter { it.second != null } // still Iterable<Pair<A, Int?>> but we can be sure the Int is not null
  .map { Pair(it.first, it.second!!) } // now it is Iterable<Pair<A, Int>>
  .toMap()

Is there any better way?

[Chantry Cargill]

iterable.mapNotNull { thing ->
  f(thing)?.let { thing to it }
}

[James Fagan]

iterable
  .associateWith { f(it) }
  .filterValues { it != null }

[diesieben07]

James that still produces a Map<A, Int?> instead of Map<A, Int>

[James Fagan]

True, in this case I think its fine to then cast it to Map<A, Int>

[James Fagan]

Or something like:

iterable
  .associateWith { f(it) }
  .filterValues { it != null }
  .mapValues { it ?: 0 }

[diesieben07]

Unchecked casts should be avoided if you can...

[James Fagan]

IMO the cast is fine when it's guaranteed to be safe 🤷‍♂️

[Xuc Xiem]

The cast is fine, however IntelliJ will give a warning, right? Then I don't know which warnings are good, which are bad.
The iterable.mapNotNull { thing -> f(thing)?.let { thing to it } } is excellent. I always wonder what's the equivalent of Scala's .collect in Kotlin. mapNotNull ?.let might not be that powerful but good enough.

[diesieben07]

I think mapNotNull is the closest equivalent