associateByTo
所在位置是kotlin.sequences.associateByTo
,其相關用法介紹如下。
用法一
inline fun <T, K, M : MutableMap<in K, in T>> Sequence<T>.associateByTo(
destination: M,
keySelector: (T) -> K
): M
使用鍵值對填充並返回 destination 可變映射,其中鍵由應用於給定序列的每個元素的 keySelector 函數提供,值是元素本身。
如果任意兩個元素具有由keySelector 返回的相同鍵,則將最後一個元素添加到Map中。
操作是 terminal
。
例子:
import kotlin.test.*
fun main(args: Array<String>) {
//sampleStart
data class Person(val firstName: String, val lastName: String) {
override fun toString(): String = "$firstName $lastName"
}
val scientists = listOf(Person("Grace", "Hopper"), Person("Jacob", "Bernoulli"), Person("Johann", "Bernoulli"))
val byLastName = mutableMapOf<String, Person>()
println("byLastName.isEmpty() is ${byLastName.isEmpty()}") // true
scientists.associateByTo(byLastName) { it.lastName }
println("byLastName.isNotEmpty() is ${byLastName.isNotEmpty()}") // true
// Jacob Bernoulli does not occur in the map because only the last pair with the same key gets added
println(byLastName) // {Hopper=Grace Hopper, Bernoulli=Johann Bernoulli}
//sampleEnd
}
輸出:
byLastName.isEmpty() is true byLastName.isNotEmpty() is true {Hopper=Grace Hopper, Bernoulli=Johann Bernoulli}
用法二
inline fun <T, K, V, M : MutableMap<in K, in V>> Sequence<T>.associateByTo(
destination: M,
keySelector: (T) -> K,
valueTransform: (T) -> V
): M
使用鍵值對填充並返回destination 可變映射,其中鍵由keySelector 函數提供,值由應用於給定序列元素的valueTransform 函數提供。
如果任意兩個元素具有由keySelector 返回的相同鍵,則將最後一個元素添加到Map中。
操作是 terminal
。
例子:
import kotlin.test.*
fun main(args: Array<String>) {
//sampleStart
data class Person(val firstName: String, val lastName: String)
val scientists = listOf(Person("Grace", "Hopper"), Person("Jacob", "Bernoulli"), Person("Johann", "Bernoulli"))
val byLastName = mutableMapOf<String, String>()
println("byLastName.isEmpty() is ${byLastName.isEmpty()}") // true
scientists.associateByTo(byLastName, { it.lastName }, { it.firstName} )
println("byLastName.isNotEmpty() is ${byLastName.isNotEmpty()}") // true
// Jacob Bernoulli does not occur in the map because only the last pair with the same key gets added
println(byLastName) // {Hopper=Grace, Bernoulli=Johann}
//sampleEnd
}
輸出:
byLastName.isEmpty() is true byLastName.isNotEmpty() is true {Hopper=Grace, Bernoulli=Johann}
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注:本文由純淨天空篩選整理自kotlinlang.org大神的英文原創作品 kotlin.sequences.associateByTo。非經特殊聲明,原始代碼版權歸原作者所有,本譯文未經允許或授權,請勿轉載或複製。