is there a built-in method that lets me filter a `Map<K,V?>` to `Map<K,V>`? I.e. filter ...

# announcements

[frogger]

is there a built-in method that lets me filter a Map<K,V?> to Map<K,V>? I.e. filter all null values and cast the map?

[Ryan]

what is the difference?

[Ryan]

one can have null values?

[frogger]

Yes, the input can have null values for V, the second map not

[Vampire]

What would be the benefit?
Retrieving a value from a map is always nullable, as the key might be absent.

[Vampire]

To just filter out null values you can do .filterValues { it != null }

[Vampire]

Otherwise the best I can up with is .filterValues { it != null }.mapValues { it.value as V }

[Vampire]

Or as extension function

fun <K, V> Map<K, V?>.filterValuesNotNull() =
        filterValues { it != null }.mapValues { it.value as V }

[Tobias Berger]

There isn't a built in function for this, but you can create one like shown by @Vampire
For those wondering: it can make a difference, depending on how you use it.
• a check for myKey in myMap can return true, but myMap[myKey] would still return null
• when using entries, forEach or something alike, you can get entries with null values
• Basically everything except for the simple get call behaves differently

[frogger]

exactly that was my intention. the additional mapValues variant looks mjuch nicer than the cast I did, will try that, thanks!