Hi guys... Is there a way to sort a map/Hashmap us...

# announcements

[linus muema]

Hi guys...
Is there a way to sort a map/Hashmap using both the keys and values.
For instance:

[Elijah=51, Chloe=144, Natalie=207, Jayden=390, Elizabeth=485, Matthew=485]

In this map, I would like values to be sorted in a descending order first. Then sort the keys in an alphabetical order.
i.e Elizabeth must appear before Matthew even though their values are the same.
🤷‍♂️

[Niklas Gürtler]

Hashmap can't be sorted at all because of how it works... You can use a TreeMap to define your custom sorting order

[Marc Knaup]

val map = mapOf(
    "Elijah" to 51, "Chloe" to 144, "Natalie" to 207, "Jayden" to 390, "Matthew" to 485, "Elizabeth" to 485,
)
val sortedMap = map
    .toList()
    .sortedWith(compareBy<Pair<String,Int>> { it.second }.thenBy { it.first })
    .toMap()

[linus muema]

@Marc Knaup, your solution results to

{Elijah=51, Chloe=144, Natalie=207, Jayden=390, Elizabeth=485, Matthew=485}

[Niklas Gürtler]

(note that the toMap does not return a HashMap which does not have its fast amortized O(1) look up time)

[Marc Knaup]

@linus muema I’ve missed the “descending” 🙂

val map = mapOf(
    "Elijah" to 51, "Chloe" to 144, "Natalie" to 207, "Jayden" to 390, "Matthew" to 485, "Elizabeth" to 485,
)
val sortedMap = map
    .toList()
    .sortedWith(compareByDescending<Pair<String,Int>> { it.second }.thenBy { it.first })
    .toMap()

[Marc Knaup]

@Niklas Gürtler toMap() uses LinkedHashMap which should also have O(1) lookup. It just uses more memory to maintain order.

[linus muema]

@Marc Knaup
It works...Thanks a lot K

[Niklas Gürtler]

Right, that's basically a HashMap + Linked list so technically the HashMap is still not sorted 😉 but right, that's a good solution

[Ivan Pavlov]

Could it be a bit simplified using entries instead of intermediate toList?

[Marc Knaup]

Then you won’t have a convenient toMap() at the end which operates on Iterable<Pair<…>>

[Ivan Pavlov]

Got it, thank you

[Marc Knaup]

@Ivan Pavlov it would look like this:

val sortedMap = map
        .entries
        .sortedWith(compareByDescending<Map.Entry<String, Int>> { it.key }.thenBy { it.value })
        .associate { it.key to it.value }

[Ivan Pavlov]

Personally I prefer associateBy version which doesn't create intermediate pairs for each entry too :)

[Marc Knaup]

associateBy only allows you to specify the key, not the value.

[Ivan Pavlov]

No, there is overload which accepts both keySelector and valueTransform

[Marc Knaup]

Ah yeah, you’re right 🙂