Kotlin Documentation | Map-specific operations

Kotlin Documentation 시리즈에 대해

Category: Standard library - Collections

문서 링크: https://kotlinlang.org/docs/map-operations.html

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Retrieve keys and values

• get(), this[key]: 찾을 수 없는 경우 null을 반환한다.
• getOrElse(), getOrDefault()
• getValue(): 찾을 수 없는 경우 예외를 던진다.

val numbersMap = mapOf("one" to 1, "two" to 2, "three" to 3)
println(numbersMap.get("one"))
println(numbersMap["one"])
println(numbersMap.getOrDefault("four", 10))
println(numbersMap["five"])               // null
//numbersMap.getValue("six")      // exception!

1
1
10
null

• this.keys, this.values

Filter

• filter()

val numbersMap = mapOf("key1" to 1, "key2" to 2, "key3" to 3, "key11" to 11)
val filteredMap = numbersMap.filter { (key, value) -> key.endsWith("1") && value > 10}

• filterKeys()
• filterValues()

val numbersMap = mapOf("key1" to 1, "key2" to 2, "key3" to 3, "key11" to 11)
val filteredKeysMap = numbersMap.filterKeys { it.endsWith("1") }
val filteredValuesMap = numbersMap.filterValues { it < 10 }

Plus and minus operators

val numbersMap = mapOf("one" to 1, "two" to 2, "three" to 3)
println(numbersMap + Pair("four", 4))
println(numbersMap + Pair("one", 10))
println(numbersMap + mapOf("five" to 5, "one" to 11))

{one=1, two=2, three=3, four=4}
{one=10, two=2, three=3}
{one=11, two=2, three=3, five=5}

val numbersMap = mapOf("one" to 1, "two" to 2, "three" to 3)
println(numbersMap - "one")
println(numbersMap - listOf("two", "four"))

{two=2, three=3}
{one=1, three=3}

Map write operations

Rules:

• key는 변경할 수 없으며, value는 변경할 수 있다.
• key-value는 한 쌍이다.(a single value associated with the key)

Add and update entries

• put(), putAll(): key가 이미 있는 경우 덮어쓴다.

numbersMap.put("three", 3)
numbersMap.putAll(setOf("four" to 4, "five" to 5))

• plusAssign(), +=
• this[], set()

Remove entries

• remove()

val numbersMap = mutableMapOf("one" to 1, "two" to 2, "three" to 3)
numbersMap.remove("one")
numbersMap.remove("three", 4)            //doesn't remove anything

val numbersMap = mutableMapOf("one" to 1, "two" to 2, "three" to 3, "threeAgain" to 3)
numbersMap.keys.remove("one")
println(numbersMap)
numbersMap.values.remove(3)
println(numbersMap)

• minusAssign(), -=