如何使用scala在列表中创建一组相同的元素？

Question

假设我们有一个案例班学生

case class Student(name: String,roll: String)

和学生名单

List(Student("a","123"),Student("b","345"),Student("a","678"),Student("b","321"))

我想建立同名的群组，例如

List(Student("a","123"),Student("a","678")) , List(Student("b","345"),Student("b","321"))

如何使用Scala做到这一点？

Answer 1

这是一种实现方法：

case class Student(name: String,roll: String)

val list = List(Student("a","123"),Student("b","345"),Student("a","678"),Student("b","321"))

val groupedList = list.groupBy(_.name).values.toList
// groupedList: List[List[Student]] = List(
//   List(Student(b,345), Student(b,321)), List(Student(a,123), Student(a,678))
// )

Answer 2

如果您要查找List[List[Student]]则需要将Student分组为列表

val groups = List( List(Student("a","123"),Student("a","678")), List(Student("b","345"),Student("b","321")) )

如果您正在寻找Map[String, List[Student]]

val groups = Map("a" -> List(Student("a","123"),Student("a","678")), "b" -> List(Student("b","345"),Student("b","321")))

Answer 3

您可以在列表上使用groupBy ，然后提取值

scala> case class Student(name: String,roll: String)
defined class Student

scala> val l = List(Student("a","123"),Student("b","345"),Student("a","678"),Student("b","321"))
l: List[Student] = List(Student(a,123), Student(b,345), Student(a,678), Student(b,321))

scala> l.groupBy(_.name).values.toList
res0: List[List[Student]] = List(List(Student(b,345), Student(b,321)), List(Student(a,123), Student(a,678)))