C# List<> Sort by x then y


Question

Similar to List<> OrderBy Alphabetical Order, we want to sort by one element, then another. we want to achieve the functional equivalent of

SELECT * from Table ORDER BY x, y  

We have a class that contains a number of sorting functions, and we have no issues sorting by one element.
For example:

public class MyClass {
    public int x;
    public int y;
}  

List<MyClass> MyList;

public void SortList() {
    MyList.Sort( MySortingFunction );
}

And we have the following in the list:

Unsorted     Sorted(x)     Desired
---------    ---------    ---------
ID   x  y    ID   x  y    ID   x  y
[0]  0  1    [2]  0  2    [0]  0  1
[1]  1  1    [0]  0  1    [2]  0  2
[2]  0  2    [1]  1  1    [1]  1  1
[3]  1  2    [3]  1  2    [3]  1  2

Stable sort would be preferable, but not required. Solution that works for .Net 2.0 is welcome.

1
86
5/23/2017 12:32:18 PM

Accepted Answer

Do keep in mind that you don't need a stable sort if you compare all members. The 2.0 solution, as requested, can look like this:

 public void SortList() {
     MyList.Sort(delegate(MyClass a, MyClass b)
     {
         int xdiff = a.x.CompareTo(b.x);
         if (xdiff != 0) return xdiff;
         else return a.y.CompareTo(b.y);
     });
 }

Do note that this 2.0 solution is still preferable over the popular 3.5 Linq solution, it performs an in-place sort and does not have the O(n) storage requirement of the Linq approach. Unless you prefer the original List object to be untouched of course.

98
10/5/2014 1:56:59 AM

For versions of .Net where you can use LINQ OrderBy and ThenBy (or ThenByDescending if needed):

using System.Linq;
....
List<SomeClass>() a;
List<SomeClass> b = a.OrderBy(x => x.x).ThenBy(x => x.y).ToList();

Note: for .Net 2.0 (or if you can't use LINQ) see Hans Passant answer to this question.


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