CODEWITHSUNDEEP
c#linq
Shawn
Shawn

Reputation: 869

C# Linq Custom Sort

I have a query in linqtosql that returns a LabelNumber:

var q = from list in db.Lists
        select list.LabelNumber;

var q then becomes an IEnumerable<string> with elements like this:

{"1","2","2.A","2.B","3","3.A","3.B"}

I basically want to order the elements as they appear above, but I can't use the OrderBy(x=>x.LabelNumber) because "10" would get placed after "1" and before "2".

I assume I have to write a custom comparator function, but how do I do this with linq?

Edit: I think all of the answers below will work, but one caveat must be added to all responses.

If you are using Linq2SQL you cannot use array indexes within the query. To overcome this, you should have two queries. One that reads from SQL. The second does the ordering:

var q = from list in db.Lists
            select list.LabelNumber;

var q2 = q.AsEnumerable()
          .OrderBy(x => int.Parse(x.LabelNumber.Split('.')[0]))
          .ThenBy(x => x.Number
                        .Contains(".") ? 
                              x.LabelNumber.Split('.')[1].ToString() 
                              : 
                              string.Empty);

Upvotes: 6

Views: 5500

Answers (4)

Michael Kropat
Michael Kropat

Reputation: 15207

OrderBy(x=>x.LabelNumber, new AlphanumComparator())

where AlphanumComparator is the excellent Alphanum natural sort algorithm by David Koelle. No need to reinvent the wheel.

If you're gonna use the C# version change it to:

AlphanumComparator : IComparer<string>

and 

public int Compare(string x, string y)

Upvotes: 13

Jeff Mercado
Jeff Mercado

Reputation: 134801

You probably don't have to write a custom comparer. If all your labels are in the form number.letter, you could use this.

var query = from list in db.Lists
            let split = list.LabelNumber.Split('.')
            let order = split.Length == 1
                ? new { a = int.Parse(split[0]), b = String.Empty }
                : new { a = int.Parse(split[0]), b = split[1] }
            orderby order.a, order.b
            select list.LabelNumber;

If you need more control, you could always convert the sortby fields (a and b) to the appropriate types rather than ints and strings.

If this is LINQ-to-SQL, this actually won't work since some methods used here are not supported. Here's a LINQ-to-SQL friendly version. It won't yield the prettiest query, but it will work.

var query = from list in db.Lists
            let dot = list.LabelNumber.IndexOf('.')
            let name = list.LabelNumber
            let order = dot == -1
                ? new { a = Convert.ToInt32(name.Substring(0, dot)), b = String.Empty }
                : new { a = Convert.ToInt32(name.Substring(0, dot)), b = name.Substring(dot+1) }
            orderby order.a, order.b
            select list.LabelNumber;

Upvotes: 9

Thorin Oakenshield
Thorin Oakenshield

Reputation: 14662

Here is my contribution.. using Regular Expression and LAMBDA expression

List<String> Lst = new List<string> { "1", "2", "2.A","10.A", "2.C", "3", "3.A", "3.B","2.B","11.D" };
Lst = Lst.Select(X => new
        {
            Number = int.Parse( Regex.Match(X, @"([0-9]*).?([a-zA-Z]*)").Groups[1].Value),
            Strings=Regex.Match(X, @"([0-9]*).?([a-zA-Z]*)").Groups[2].Value,
            OriginalString = X
        }).OrderBy(X => X.Number).ThenBy(X=>X.Strings)
        .Select(X => X.OriginalString).ToList();

Output: 

"1"
"2"
"2.A"
"2.B"
"2.C"
"3"
"3.A"
"3.B"
"10.A"
"11.D"

Upvotes: 0

Cheng Chen
Cheng Chen

Reputation: 43503

If you are sure that q is well-formatted and sequenced:

var result = q.OrderBy(x => int.Parse(x.Split('.')[0]));

Upvotes: 1

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