CODEWITHSUNDEEP
kotlin
Marlock
Marlock

Reputation: 285

Increase value in mutable map

I created a mutableMap<String, Int> and created a record "Example" to 0. How can I increase value, f.e. to 0 + 3 ?

Upvotes: 19

Views: 12438

Answers (4)

Wael Ellithy
Wael Ellithy

Reputation: 119

You can define

fun <K> MutableMap<K, Int>.inc(key: K): Int = merge(key, 1, Math::addExact)!!

So you can so something like

map.inc("Example")

Upvotes: 2

Kirill Groshkov
Kirill Groshkov

Reputation: 1771

How I do it:

val map = mutableMapOf<String, Int>()

map[key] = (map[key] ?: 0) + 1

Upvotes: 13

Dushyant Singh
Dushyant Singh

Reputation: 1607

You can use getOrDefault if API level is greater than 23. Otherwise you can use elvis operator

val map = mutableMapOf<String,Int>()
val value = map["Example"] ?: 0
map["Example"] = value + 3

Upvotes: 1

Rene
Rene

Reputation: 6258

You could use the getOrDefault function to get the old value or 0, add the new value and assign it back to the map.

val map = mutableMapOf<String,Int>()
map["Example"] = map.getOrDefault("Example", 0) + 3

Or use the merge function from the standard Map interface.

val map = mutableMapOf<String,Int>()
map.merge("Example", 3) {
    old, value -> old + value
}

Or more compact:

map.merge("Example",3, Int::plus)

Upvotes: 42

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