Set

Set沒有順序，不允許重複值的集合。

唯讀Set

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val set1: Set<String> = setOf("Mary", "Mary", "Mary", "Alice")
println(set1)

[Mary, Alice]

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val mutableSet1: MutableSet<String> = mutableSetOf("Mary", "Bill", "Jery")

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println(set1.elementAt(0))
println(set1.elementAtOrElse(5) { "no data" })
println(set1.elementAtOrNull(5) ?: "no data")

Mary
no data
no data

Set沒有順序，因此沒辦法用索引進行修改。

新增

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val mutableSet1: MutableSet<String> = mutableSetOf("Mary", "Bill", "Jery")
mutableSet1.add("May")
mutableSet1 += "Gigi"
println(mutableSet1)

刪除

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mutableSet1.remove("Bill")
mutableSet1 -= "Mary"
println(mutableSet1)

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val list1 = listOf("Alice", "Alice", "Alice","Mary")
    .toSet()
    .toList()
println("list1 = $list1")

list1 = [Alice, Mary]

distinct也有同樣效果。

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val list2 = listOf("Alice", "Alice", "Alice","Mary")
    .distinct()
println("list2 = $list2")

list2 = [Alice, Mary]