Question

I have a list of strings. Each string follows the pattern “{Path}\UpdateTo{Version}-{Order}”.

I need to sort the list such that the lowest version numbers are at the top. In the case when there is multiple files with the same version number then an optional order parameter is appended. If an order is present on any of the strings then it should appear above the strings with the same version number that do not have an order number.

For example, give the following list (note the items are randomly ordered):

var files = new List<string>() {
    @"C:\Migrations\UpdateTo1.2-2",
    @"C:\Migrations\UpdateTo1.5-2",
    @"C:\Migrations\UpdateTo1.2",
    @"C:\Migrations\UpdateTo1.4",
    @"C:\Migrations\UpdateTo1.1",
    @"C:\Migrations\UpdateTo1.5",
    @"C:\Migrations\UpdateTo1.2-1",
    @"C:\Migrations\UpdateTo1.5-1"
};

The result would be:

var files = new List<string>() {
    @"C:\Migrations\UpdateTo1.1",
    @"C:\Migrations\UpdateTo1.2-1",
    @"C:\Migrations\UpdateTo1.2-2",
    @"C:\Migrations\UpdateTo1.2",
    @"C:\Migrations\UpdateTo1.4",
    @"C:\Migrations\UpdateTo1.5-1",
    @"C:\Migrations\UpdateTo1.5-2",
    @"C:\Migrations\UpdateTo1.5"
}

I’ve been trying with all sorts of ideas but so far my attempts have been a complete mess. I’d appreciate it if someone could help. Thanks

Answer 1

I used a temporary class to handle the parsing and the comparisons to get the desired output. I’ve included code that gets everything back to how you requested it but the “temporary” class introduced may have more value to you over just the paths (?).

Usage:

var sorted = files.Select(f => new UpdateTo(f))
    .OrderBy(u => u)
    .Select(u => u.Path)
    .ToArray();

The code:

class UpdateTo : IComparable<UpdateTo>
{
    public decimal Version { get; private set; }
    public int Order { get; private set; }
    public string Path { get; private set; }

    private const string Prefix = "UpdateTo";

    public UpdateTo(string path)
    {
        /* No error-checking here -- BEWARE!! */
        Path = path;

        string toParse = Path.Substring(Path.IndexOf(Prefix, StringComparison.InvariantCultureIgnoreCase) + Prefix.Length);
        var split = toParse.Split('-');

        Version = decimal.Parse(split[0]);
        Order = split.Length == 2 ? int.Parse(split[1]) : int.MaxValue;
    }

    public int CompareTo(UpdateTo other)
    {
        int versionCompare = Version.CompareTo(other.Version);
        return versionCompare == 0 ? Order.CompareTo(other.Order) : versionCompare;
    }
}

And the test…

[Test]
public void ListSort()
{
    const string first = @"C:\Migrations\UpdateTo1.1";
    const string second = @"C:\Migrations\UpdateTo1.2-1";
    const string third = @"C:\Migrations\UpdateTo1.2-2";
    const string fourth = @"C:\Migrations\UpdateTo1.2";
    const string fifth = @"C:\Migrations\UpdateTo1.4";
    const string sixth = @"C:\Migrations\UpdateTo1.5-1";
    const string seventh = @"C:\Migrations\UpdateTo1.5-2";
    const string eighth = @"C:\Migrations\UpdateTo1.5";

    var files = new List<string>{third, seventh, fourth, fifth, first, eighth, second, sixth};

    var sorted = files.Select(f => new UpdateTo(f))
        .OrderBy(u => u)
        .Select(u => u.Path)
        .ToArray();

    Assert.AreEqual(first, sorted[0]);
    Assert.AreEqual(second, sorted[1]);
    Assert.AreEqual(third, sorted[2]);
    Assert.AreEqual(fourth, sorted[3]);
    Assert.AreEqual(fifth, sorted[4]);
    Assert.AreEqual(sixth, sorted[5]);
    Assert.AreEqual(seventh, sorted[6]);
    Assert.AreEqual(eighth, sorted[7]);
}