如何在Scala中按两个字段对列表进行排序？

Question

如何在Scala中按两个字段对列表进行排序,在本例中我将按lastName和firstName排序？

case class Row(var firstName: String, var lastName: String, var city: String)

var rows = List(new Row("Oscar", "Wilde", "London"),
                new Row("Otto",  "Swift", "Berlin"),
                new Row("Carl",  "Swift", "Paris"),
                new Row("Hans",  "Swift", "Dublin"),
                new Row("Hugo",  "Swift", "Sligo"))

rows.sortBy(_.lastName)

我尝试这样的事情

rows.sortBy(_.lastName + _.firstName)

但它不起作用.所以我很好奇一个好的,简单的解决方案.

Answer 1

rows.sortBy(r => (r.lastName, r.firstName))

Answer 2

rows.sortBy (row => row.lastName + row.firstName)

如果要按合并的名称排序,如问题中所示,或者

rows.sortBy (row => (row.lastName, row.firstName))

如果你想先按lastName排序,那么firstName; 与较长的名字相关(Wild,Wilder,Wilderman).

如果你写

rows.sortBy(_.lastName + _.firstName)

有2个下划线,该方法需要两个参数:

<console>:14: error: wrong number of parameters; expected = 1
       rows.sortBy (_.lastName + _.firstName)
                               ^

Answer 3

通常,如果使用稳定的排序算法,则只需按一个键排序,然后按下一个键排序.

rows.sortBy(_.firstName).sortBy(_.lastName)

最终结果将按姓氏排序,然后按名字排序.