Linq中的对象自定义比较器

Question

I have a List.

Where T is a class have properties like int and other parameters

Eg

  ID Name

  1  Apple
  2  Banana
  3  Test

Now i have another List which specify order

Like 2,1,3

So i want to sort them using 2,1,3 like Banana,Apple and then Test

How can i implement this wihh IComaparer

Currently i tries this but it failed

 test = test.OrderBy(p=>  SortableIntList.Contains(p.ID));

Answer 1

To quickly get it working,

test = test
    .Where(p => SortableIntList.Contains(p.ID))
    .OrderBy(p => SortableIntList.IndexOf(p.ID));

To make it more efficient, you may want to store your sort order in a dictionary (ID => position) and then call it like

var SortableIntDictionary = SortableIntList
    .Select((ID, Index) => new { ID, Index })
    .ToDictionary(p => p.ID, p => p.Index);
test = test
    .Where(p => SortableIntDictionary.ContainsKey(p.ID))
    .OrderBy(p => SortableIntDictionary[p.ID]);

Answer 2

Try this, no need for comparer

 // Setup test data
 var orderList = new List<int> { 2, 1, 3 };

 var stuffList = new List<Stuff> { 
            new Stuff { Id = 1, Name = "Apple" },
            new Stuff { Id = 2, Name = "Banana" },
            new Stuff { Id = 3, Name = "Test" }
        };

 // Do sort according to list
 var result = orderList.Select(idx => stuffList.Where(s => s.Id == idx));

Edit: It may be faster to create an ID-lookup:

var stuffDictionary = stuffList.ToDictionary(s => s.ID, s => s);
var result = orderList.Where(idx => stuffDictionary.ContainsKey(idx))
                      .Select(idx => stuffDictionary[idx]);