scala 如何按两个字段对Scala中的列表进行排序？
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How to sort a list in Scala by two fields?
提问by Twistleton
how to sort a list in Scala by two fields, in this example I will sort by lastName and firstName?
如何按两个字段对 Scala 中的列表进行排序，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)
I try things like this
我尝试这样的事情
rows.sortBy(_.lastName + _.firstName)
but it doesn't work. So I be curious for a good and easy solution.
但它不起作用。所以我很好奇一个好的和简单的解决方案。
回答by senia
rows.sortBy(r => (r.lastName, r.firstName))
回答by user unknown
rows.sortBy (row => row.lastName + row.firstName)
If you want to sort by the merged names, as in your question, or
如果您想按合并名称排序，如您的问题，或
rows.sortBy (row => (row.lastName, row.firstName))
if you first want to sort by lastName, then firstName; relevant for longer names (Wild, Wilder, Wilderman).
如果您首先想按姓氏排序，则按名字排序；与较长的名称相关（Wild、Wilder、Wilderman）。
If you write
如果你写
rows.sortBy(_.lastName + _.firstName)
with 2 underlines, the method expects two parameters:
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)
^
回答by Marcin
In general, if you use a stable sorting algorithm, you can just sort by one key, then the next.
通常，如果您使用稳定的排序算法，则可以只按一个键排序，然后再按下一个键排序。
rows.sortBy(_.firstName).sortBy(_.lastName)
The final result will be sorted by lastname, then where that is equal, by firstname.
最终结果将按姓氏排序，然后按名字排序。
回答by spreinhardt
Perhaps this works only for a List of Tuples, but
也许这仅适用于元组列表，但是
scala> var zz = List((1, 0.1), (2, 0.5), (3, 0.6), (4, 0.3), (5, 0.1))
zz: List[(Int, Double)] = List((1,0.1), (2,0.5), (3,0.6), (4,0.3), (5,0.1))
scala> zz.sortBy( x => (-x._2, x._1))
res54: List[(Int, Double)] = List((3,0.6), (2,0.5), (4,0.3), (1,0.1), (5,0.1))
appears to work and be a simple way to express it.
似乎有效并且是一种简单的表达方式。
