Custom sort of List<string>

I have a List<string>, where the entries are locations, like "010101", "010102", "010201", ..., with following meaning:

First two characters : floor
Next two characters : lane
Last two characters : entry in lane

Normal sorting reveals a list like the following:

I would like a custom sorting, where:

on floor "01", the sorting is done in a normal way:
```
  010101
  010102
  010103
  010201
  010202
```
on floor "02", the sorting is done in a reversed way for the lane, but not for the entry in lane, so something like:
```
  ...
  020201
  020202
  020203
  020204
  020101
  020102
```

Here on the site, I've found the IEnumerable as a solution, but this only works for List<T> where T is a new class. This is not relevant here, as I'm dealing with "simple" strings.
I've also found the Enumerable as a solution, but this also doesn't work, because the list of possible strings is far too large (not enumerable) and I'd prefer a flexible solution.

Does anybody have an idea?

Thanks in advance

Solution

There are multiple ways to achieve the desired behavior, e.g. using a Comparison<string>:

var input = new List<string>() { "010101", "010102", "010103", "010201", "010202", "020101", "020102", "020201", "020202", "020203", "020204" };

Comparison<string> comparison = (s1, s2) =>
{
    if (s1 == null) throw new ArgumentNullException(nameof(s1));
    if (s2 == null) throw new ArgumentNullException(nameof(s2));
    if (s1.Length != 6 || s2.Length != 6) throw new ArgumentOutOfRangeException();

    // Compare floor (first 2 digits)
    var floor1 = s1.Substring(0, 2);
    var floor2 = s2.Substring(0, 2);
    var result = floor1.CompareTo(floor2);
    if (result != 0) return result;

    // Compare lane (middle 2 digits)
    var lane1 = s1.Substring(2, 2);
    var lane2 = s2.Substring(2, 2);
    // Special case: in floor 02, reverse order of lanes
    result = floor1 == "02"
       ? lane2.CompareTo(lane1) 
       : lane1.CompareTo(lane2);
    if (result != 0) return result;

    // Compare entry (last 2 digits)
    return s1.Substring(4, 2).CompareTo(s2.Substring(4, 2));
};

// Sort the list using the comparison defined before
input.Sort(comparison);