kotlin - groupBy Kotlin 中的多个字段和求和值

Question

假设我的数据如下所示

data class Student(val name: String, val room: Int, val sex: String, val height: Int, val weight: Double){}

我有一份学生名单

val students = listOf(
     Student("Max", 1, "M", 165, 56.8),
     Student("Mint", 1, "F", 155, 53.2),
     Student("Moss", 1, "M", 165, 67.3),
     Student("Michael", 2, "M", 168, 65.6),
     Student("Minnie", 2, "F", 155, 48.9),
     Student("Mickey", 1, "M", 165, 54.1),
     Student("Mind", 2, "F", 155, 51.2),
     Student("May", 1, "F", 155, 53.6))

我的目标是将房间、性别和高度相同的学生分组，然后将他们的体重相加

最终的名单应该是这样的

{
Student(_, 1, "M", 165, <sum of weight of male students who is in 1st room with height 165>),
Student(_, 1, "F", 155, <sum of weight of female students who is in 1st room with height 155>),
...
}

(学生姓名可省略)

我已经看过 Nested groupBy in Kotlin但它没有回答我的问题。

Answer 1

当您需要按多个字段分组时，您可以使用Pair、Triple 或您的自定义数据类作为分组键

val result = students
    .groupingBy { Triple(it.room, it.sex, it.height) }
    .reduce { _, acc, element ->
        acc.copy(name = "_", weight = acc.weight + element.weight)
    }
    .values.toList()