本文方法及代码示例基于Kotlin 2.1.20 Released
groupByTo
所在包 kotlin.text.groupByTo
,其相关用法介绍如下:
用法一
kotlin
inline fun <K, M : MutableMap<in K, MutableList<Char>>> CharSequence.groupByTo(
destination: M,
keySelector: (Char) -> K
): M
通过应用于每个字符的给定keySelector 函数返回的键对原始字符序列的字符进行分组,并将与对应字符列表关联的每个组键放入destination 映射。
示例代码:
kotlin
import kotlin.test.*
fun main(args: Array<String>) {
//sampleStart
val words = listOf("a", "abc", "ab", "def", "abcd")
val byLength = words.groupBy { it.length }
println(byLength.keys) // [1, 3, 2, 4]
println(byLength.values) // [[a], [abc, def], [ab], [abcd]]
val mutableByLength: MutableMap<Int, MutableList<String>> = words.groupByTo(mutableMapOf()) { it.length }
// same content as in byLength map, but the map is mutable
println("mutableByLength == byLength is ${mutableByLength == byLength}") // true
//sampleEnd
}
// 输出
[1, 3, 2, 4]
[[a], [abc, def], [ab], [abcd]]
mutableByLength == byLength is true
返回destination Map。
用法二
kotlin
inline fun <K, V, M : MutableMap<in K, MutableList<V>>> CharSequence.groupByTo(
destination: M,
keySelector: (Char) -> K,
valueTransform: (Char) -> V
): M
由应用于原始字符序列的每个字符的valueTransform 函数返回的值由应用于字符的给定keySelector 函数返回的键分组,并将每个组键与对应的列表关联到destination 映射值。
示例代码:
kotlin
import kotlin.test.*
fun main(args: Array<String>) {
//sampleStart
val nameToTeam = listOf("Alice" to "Marketing", "Bob" to "Sales", "Carol" to "Marketing")
val namesByTeam = nameToTeam.groupBy({ it.second }, { it.first })
println(namesByTeam) // {Marketing=[Alice, Carol], Sales=[Bob]}
val mutableNamesByTeam = nameToTeam.groupByTo(HashMap(), { it.second }, { it.first })
// same content as in namesByTeam map, but the map is mutable
println("mutableNamesByTeam == namesByTeam is ${mutableNamesByTeam == namesByTeam}") // true
//sampleEnd
}
// 输出
{Marketing=[Alice, Carol], Sales=[Bob]}
mutableNamesByTeam == namesByTeam is true
返回destination Map。
相关方法
- Kotlin contentToString用法及代码示例
- Kotlin dropWhile用法及代码示例
- Kotlin distinct用法及代码示例
- Kotlin code用法及代码示例
- Kotlin Map:mapOf()用法及代码示例
- Kotlin distinctBy用法及代码示例
- Kotlin digitToChar用法及代码示例
- Kotlin ifBlank用法及代码示例
- Kotlin all用法及代码示例
- Kotlin digitToIntOrNull用法及代码示例
- Kotlin dropLast用法及代码示例
- Kotlin dropLastWhile用法及代码示例
- Kotlin associateBy用法及代码示例
- Kotlin groupingBy用法及代码示例
- Kotlin groupBy用法及代码示例
- Kotlin getOrElse用法及代码示例
- Kotlin getOrPut用法及代码示例