在LINQ排序的IEnumerable

Question

可能重複：
Sorting an IEnumerable in LINQ

是否可以解決這一個不使用.ToList（）？

請參閱下面的代碼。

下面的代碼將產生此輸出。

{ id = 1, name = "sample 1", list = {'a','f','d'}},   
    { id = 5, name = "sample 1", list = {'a','f','c'}}, 
    { id = 2, name = "sample 1", list = {'g','b'}}, 
    { id = 4, name = "sample 1", list = {'i','e','h'}}, 
    { id = 6, name = "sample 1", list = {'d','b','c'}}, 
    { id = 3, name = "sample 1", list = {'h','i','c'}}, 

感謝

RJ

IEnumerable<extra> eList = new List<extra>() 
{ 
    new extra{ id = 1, text = "a"}, 
    new extra{ id = 2, text = "g"}, 
    new extra{ id = 3, text = "i"}, 
    new extra{ id = 4, text = "e"}, 
    new extra{ id = 5, text = "f"}, 
    new extra{ id = 6, text = "d"}, 
    new extra{ id = 7, text = "c"}, 
    new extra{ id = 8, text = "h"}, 
    new extra{ id = 9, text = "b"} 
}; 

IEnumerable<sample> sam = new List<sample>() 
{ 
    new sample{ id = 1, name = "sample 1", list = new List<int>{1,5,6}}, 
    new sample{ id = 2, name = "sample 2", list = new List<int>{2,9}}, 
    new sample{ id = 3, name = "sample 3", list = new List<int>{8,3,7}}, 
    new sample{ id = 4, name = "sample 4", list = new List<int>{3,4,8}}, 
    new sample{ id = 5, name = "sample 5", list = new List<int>{1,5,7}}, 
    new sample{ id = 6, name = "sample 6", list = new List<int>{6,9,7}} 
}; 

var sorted = (from d1 in sam 
       select new 
       { 
        name = d1.name, 
        id = d1.id, 
        list = 
        (
         from d2 in d1.list 
         join e in eList on d2 equals e.id 
         select e.text 
       ).OrderBy(item => item).ToList() 
       }).OrderBy(item => item.list.FirstOrDefault()); 

Answer 1

也許ThenBy會做嗎？

var sorted = (from d1 in sam 
       select new 
       { 
        name = d1.name, 
        id = d1.id, 
        list = 
        ( 
         from d2 in d1.list 
         join e in eList on d2 equals e.id 
         select e.text 
       ).OrderBy(item => item 
       }).ThenBy(item => item.list.FirstOrDefault()); 

我誤解了這個問題。爲什麼不只是刪除ToList？您可能想要.ToList（），但每次訪問集合時都要防止排序。

Answer 2

我剛剛測試了你的原始代碼，沒有'ToList'，它對項目和'extras'進行了排序就好了。你能詳細說明你到底想達到什麼嗎？證明：你的代碼沒有ToList

1 "sample 1" a d f 
5 "sample 5" a c f 
2 "sample 2" b g 
6 "sample 6" b c d 
3 "sample 3" c h i 
4 "sample 4" e h i 

結果：你的原代碼與ToList

結果

1 "sample 1" a d f <-- adf is sorted 
5 "sample 5" a c f <-- also sorted 
2 "sample 2" b g  <-- and here too 
6 "sample 6" b c d <-- yep 
3 "sample 3" c h i <-- it is! 
4 "sample 4" e h i <-- ... 
      ^
       | 
       \ aabbce is sorted, too 

看起來與我:)

至於總體思路，在沒有「ToList」的情況下用LINQ語法編寫的小問題是，JOIN將被懶惰地執行，每個項目執行一次，並且每次它將從頭構建映射/連接，而它是完全緩存和可重用。在下面的擴展語法中，我只顯式地預先創建一次映射，然後所有其他沒有使用任何實現的惰性查詢共享相同的映射。這樣，它可能是快好幾倍，並使用更少的內存：

var mapping = eList.ToDictionary(x => x.id, x=>x.text); 

var temps = sam.Select(s => 
    new { 
     id = s.id, 
     name = s.name, 
     stringlist = s.list.Select(id => mapping[id]).OrderBy(str => str) 
    }); 

var result = temps.OrderBy(t => t.stringlist.FirstOrDefault()); 

Answer 3

試試這個：

var sorted = (from d1 in sam 
       select new 
       { 
        name = d1.name, 
        id = d1.id, 
        list = 
        (
         from d2 in d1.list 
         join e in eList on d2 equals e.id 
         select e.text 
       ) 
       }).OrderBy(item => item.list.OrderBy(i => i).FirstOrDefault());