Question

Possible Duplicate:
Natural Sort Order in C#

I have a list with a lot of numbers in it.
But they are saved as strings because of some additional letters.

My list looks something like this:

1
10
11
11a
11b
12
2
20
21a
21c
A1
A2
...

but it should look like this

1
2
10
11a
11b
...
A1
A2
...

How do i sort my list to get this result?

Answer 1

Going by the previous comments, I would also implement a custom IComparer<T> class. From what I can gather, the structure of the items is either a number, of a combination of a number followed by a letter(s). If this is the case, the following IComparer<T> implementation should work.

public class CustomComparer : IComparer<string>
{
    public int Compare(string x, string y)
    {
        var regex = new Regex("^(d+)");

        // run the regex on both strings
        var xRegexResult = regex.Match(x);
        var yRegexResult = regex.Match(y);

        // check if they are both numbers
        if (xRegexResult.Success && yRegexResult.Success)
        {
            return int.Parse(xRegexResult.Groups[1].Value).CompareTo(int.Parse(yRegexResult.Groups[1].Value));
        }

        // otherwise return as string comparison
        return x.CompareTo(y);
    }
}

With this IComparer<T>, you’ll be able to sort your list of string by doing

var myComparer = new CustomComparer();
myListOfStrings.Sort(myComparer);

This has been tested with the following items:

2, 1, 4d, 4e, 4c, 4a, 4b, A1, 20, B2, A2, a3, 5, 6, 4f, 1a

and gives the result:

1, 1a, 2, 20, 4a, 4b, 4c, 4d, 4e, 4f, 5, 6, A1, A2, a3, B2