Question

I have the following c# code that sorts a string in a lexicographical (alphabetical) order.

string str = "ACGGACGAACT";


IEnumerable<string> sortedSubstrings =
                    Enumerable.Range(0, str.Length)
                    .Select(i => str.Substring(i))
                    .OrderBy(s => s);

Result:
0 AACT
1 ACGAACT
2 ACGGACGAACT
3 ACT
4 CGAACT
5 CGGACGAACT
6 CT
7 GAACT
8 GACGAACT
9 GACGAACT
10 T

However I want to enhance this sort by skipping the 3rd and the 4th character during the lexicographical sort process

In this case the lexicographical sort will be different to the one above.

result:
0 AA[CT
1 AC[T
2 AC[GG]ACGAACT
3 AC[GA]ACT
4 CG[GA]CGAACT
5 CG[AA]CT
6 CT
7 GA[CG]AACT
8 GA[AC]T
9 GG[AC]GAACT
10 T

how can I achieve this?

Answer 1

This can be done by tweaking the lambda passed to OrderBy. Something like this should do it:

var sortedSubstrings = 
    Enumerable.Range(0, str.Length)
    .Select(i => str.Substring(i))
    .OrderBy(s => s.Length < 3 ? s : s.Remove(2, Math.Min(s.Length - 2, 2)));

Edit: Corrected off-by-one error.