C# List<> Sort by x then y
C#.NetSortingC# Problem Overview
Similar to https://stackoverflow.com/questions/188141/c-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.
C# Solutions
Solution 1 - C#
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.
Solution 2 - C#
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.
Solution 3 - C#
The trick is to implement a stable sort. I've created a Widget class that can contain your test data:
public class Widget : IComparable
{
int x;
int y;
public int X
{
get { return x; }
set { x = value; }
}
public int Y
{
get { return y; }
set { y = value; }
}
public Widget(int argx, int argy)
{
x = argx;
y = argy;
}
public int CompareTo(object obj)
{
int result = 1;
if (obj != null && obj is Widget)
{
Widget w = obj as Widget;
result = this.X.CompareTo(w.X);
}
return result;
}
static public int Compare(Widget x, Widget y)
{
int result = 1;
if (x != null && y != null)
{
result = x.CompareTo(y);
}
return result;
}
}
I implemented IComparable, so it can be unstably sorted by List.Sort().
However, I also implemented the static method Compare, which can be passed as a delegate to a search method.
I borrowed this insertion sort method from C# 411:
public static void InsertionSort<T>(IList<T> list, Comparison<T> comparison)
{
int count = list.Count;
for (int j = 1; j < count; j++)
{
T key = list[j];
int i = j - 1;
for (; i >= 0 && comparison(list[i], key) > 0; i--)
{
list[i + 1] = list[i];
}
list[i + 1] = key;
}
}
You would put this in the sort helpers class that you mentioned in your question.
Now, to use it:
static void Main(string[] args)
{
List<Widget> widgets = new List<Widget>();
widgets.Add(new Widget(0, 1));
widgets.Add(new Widget(1, 1));
widgets.Add(new Widget(0, 2));
widgets.Add(new Widget(1, 2));
InsertionSort<Widget>(widgets, Widget.Compare);
foreach (Widget w in widgets)
{
Console.WriteLine(w.X + ":" + w.Y);
}
}
And it outputs:
0:1
0:2
1:1
1:2
Press any key to continue . . .
This could probably be cleaned up with some anonymous delegates, but I'll leave that up to you.
EDIT: And NoBugz demonstrates the power of anonymous methods...so, consider mine more oldschool :P
Solution 4 - C#
This may help you,
How to Sort C# Generic List
Solution 5 - C#
I had an issue where OrderBy and ThenBy did not give me the desired result (or I just didn't know how to use them correctly).
I went with a list.Sort solution something like this.
var data = (from o in database.Orders Where o.ClientId.Equals(clientId) select new {
OrderId = o.id,
OrderDate = o.orderDate,
OrderBoolean = (SomeClass.SomeFunction(o.orderBoolean) ? 1 : 0)
});
data.Sort((o1, o2) => (o2.OrderBoolean.CompareTo(o1.OrderBoolean) != 0
o2.OrderBoolean.CompareTo(o1.OrderBoolean) : o1.OrderDate.Value.CompareTo(o2.OrderDate.Value)));