LINQ到對象通過參數任意數量的訂貨

Question

我有Func定義排序列表：

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

我可以訂購類似的結果...

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

我當列表可以包含任意數量的順序排序時，試圖找出如何進行上述操作。可能嗎？

Answer 1

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

相同

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

，所以你只要寫一個像這樣的循環：

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

你可能想要動態地建立你的表達。這裏更多的信息：Dynamic LINQ and Dynamic Lambda expressions?

Answer 3

你應該能夠做到類似這樣

東西

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

Al ternately

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

Answer 4

請記住，LINQ執行被延期。您可以訪問的結果，做這樣的事情之前建立的表達順序：

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

Answer 5

正如其他人所說，你可以使用一個循環做到這一點。

如果你願意，你也可以使用Aggregate操作：

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

（或）

// 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);