c# - Linq to Objects 按任意数量的参数排序

Question

我有一个Func定义排序的列表：

var ordering = new List<Func<Person, IComparable>> 
                 { x => x.Surname, x => x.FirstName };

我可以用类似的东西订购结果...

people = people.OrderBy(ordering[0]).ThenBy(ordering[1]);

我试图弄清楚当列表可以包含任意数量的顺序时如何执行上述操作。可能吗？

Answer 1

people = people.OrderBy(ordering[0]).ThenBy(ordering[1]).ThenBy(ordering[2]);

是相同的

var orderedPeople = people.OrderBy(ordering[0]);
orderedPeople = orderedPeople.ThenBy(ordering[1]);
orderedPeople = orderedPeople.ThenBy(ordering[2]);
people = orderedPeople;

所以你只需写一个这样的循环：

if (ordering.Count != 0)
{
    var orderedPeople = people.OrderBy(ordering[0]);
    for (int i = 1; i < ordering.Count; i++)
    {
        orderedPeople = orderedPeople.ThenBy(ordering[i]);
    }
    people = orderedPeople;
}

Answer 2

正如其他人所提到的，您可以使用循环来执行此操作。

如果您愿意，还可以使用Aggregate运算符：

// Requires a non-empty ordering sequence.
var result2 = ordering.Skip(1)
                      .Aggregate(people.OrderBy(ordering.First()), Enumerable.ThenBy); 

（或者）

// Shorter and more "symmetric" but potentially more inefficient.
// x => true should work because OrderBy is a stable sort.
var result = ordering.Aggregate(people.OrderBy(x => true), Enumerable.ThenBy);

Answer 3

你应该能够做类似的事情

people = people.OrderBy(ordering[0])
foreach(var order in ordering.Skip(1))
{
  people = people.ThenBy(order);
}

交替

 for(i = 0; i < ordering.Count; i++)
 {
    people = i == 0 ? people.OrderBy(ordering[i]) : people.ThenBy(ordering[i]);
 }

Answer 4

请记住，LINQ 执行是延迟的。您可以在访问结果之前按顺序构建表达式，执行以下操作：

var ordered = unordered.OrderBy(ordering.First());
foreach (var orderingItem in ordering.Skip(1))
{
    ordered = ordered.ThenBy(orderingItem);
}

Answer 5

您可能希望通过动态构建您的表达来做到这一点。更多信息：动态 LINQ 和动态 Lambda 表达式？