I want to filter the list for carMakes that have a constraint on the

name

field, then reconstruct this sortedmap agian

Something like that? https://pl.kotl.in/HySGJC9UE

ahh

TreeMap

is first implementation of

SortedMap

that I found. Kotlin’s

.toSortedMap()

also creates

TreeMap

Nice!

yes that’s fine, I had changed the receiving function’s signature to Hashmap, i do

toSortedMap

inside it, i was doing it twice before, it was wrong

If I understood correctly what your snippet does, then I would recommend:

val carMakesMap = carMakes.values
    .flatten()
    .filter { carMake -> carMake.name.contains(newText, ignoreCase = true) }
    .groupBy { it.name.first() }

Or maybe:

val carMakesMap = carMakes
    .mapValues { (_, value) ->
        value.filter {carMake -> carMake.name.contains(newText, ignoreCase = true) }
    }
    .filterValues { it.isNotEmpty() }

You can avoid a lot of intermediary collections by replacing

.functionalOperator { ... }.toCustomCollectionImpl()

with

.functionalOperatorTo(CustomCollectionImpl()) { ... }

didnt understand what you suggested kevin

If you find yourself doing a functional transform like

mapValues

, and then the output collection isn't in a format that you want so you do something like

toMap(...)

or

toSortedMap()

or anything like that, you could use the version of the transform ending in

To

, like

mapValuesTo

and specify a collection to output into as the first parameter

so I wouldnt have to worry about the transformation at the end?

trying to understand the full problem. So the

Char

keys are like, the first letter in the car make? Like the map is:

[
  'a': [],
  'b': [],
  'c': [CarMake("Chevy")],
  'd': [CarMake("Dodge")],
  ...
]

?

terribly sorry, here’s the screenshot that explains what the usecase is http://snpy.in/EM3Bym

you mean you want to remove the characters that have no matches?

the keys that have values which are empty <-- thats how i think of it

carMakes
    .mapValuesTo(TreeMap()) { (_, values: List<String>) -> values.filter { it.contains(filter, ignoreCase = true) }}
    .filterTo(TreeMap()) { (_, values) -> values.isNotEmpty() }

is there something about this that wouldn't work?

i was not able to try what you suggestd, syntax was weird

I feel like you could also do

👍🏻