Order by multiple properties

Question

I have list which I want to order by like this

First by "ab"
Then by alphabetical order inside the list by "ab"
Then by "cd"
Then by alphabetical order inside the list by "cd"
Then by "ef"
Then by alphabetical order inside the list by "ef"

and then the rest by alphabetical order

I have this linq query

var groups =  profileModel.Groups.
OrderByDescending(i => i.FullName.ToLower().Contains("ab")).
ThenByDescending(i => i.FullName.ToLower().Contains("cd")).
ThenByDescending(i => i.FullName.ToLower().Contains("ef"));

How should I extend this one? Do I have to use group by?

You notice that you have multiple `First by`? Provide a Sample — Tim Schmelter, Apr 12 '18 at 09:17
Similar question https://stackoverflow.com/questions/728319/linq-orderby-against-specific-values — neildt, Apr 12 '18 at 09:17
Are you doing this on IQueriable(EF to SQL) or in memory IEnumerable — Filip Cordas, Apr 12 '18 at 09:21
Note: "then by" means "then another sort"; it isn't talking about *vertical partitions*; are you trying to describe vertical partitions? You can *implement* that by multiple sorts, but it is... very odd — Marc Gravell, Apr 12 '18 at 09:24

score 0 · Answer 1 · answered Apr 12 '18 at 09:29

0

It seems that you want this, then no need to use GroupBy:

var groupOrders = new List<string> { "ab", "cd", "ef" };

var resultList = profileModel.Groups
    .Select(x => new { ModelGroup = x, First2Letter = x.FullName.Substring(Math.Min(2, x.FullName.Length)) })
    .Select(x => new
    {
        x.ModelGroup,
        x.First2Letter,
        Index = groupOrders.FindIndex(s => s.Equals(x.First2Letter, StringComparison.OrdinalIgnoreCase))
    })
    .OrderByDescending(x => x.Index >= 0) // first all known groups
    .ThenBy(x => x.Index)
    .ThenBy(x => x.ModelGroup.FullName)
    .Select(x => x.ModelGroup)
    .ToList();

answered Apr 12 '18 at 09:29

Tim Schmelter

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maybe replace Equals with Contains ? – Florian Apr 12 '18 at 09:37
@Florian: No, `s` is the string in the list and `First2Letter` are the first two letters of each `FullName`. – Tim Schmelter Apr 12 '18 at 09:51
Right, your solution is different from what I had in mind, my bad! – Florian Apr 12 '18 at 09:56

Filip Cordas · Answer 2 · 2018-04-12T10:03:51.053

If I got the problem correctly, this will order items based on what they contain. should work in EF as well.

var orderItems = from item in profileModel.Groups
                 let name = item.FullName.ToLower()
                 orderby (name.Contains("ab") ? 1 : 0) + (name.Contains("cd") ? 0.1 : 0) + (name.Contains("ef") ? 0.01 : 0) descending
                 select item;

EDIT After rereading the problem this might be the right solution

var orderItems = from item in profileModel.Groups
                 let name = item.FullName.ToLower()
                 let order = name.Contains("ab") ? 3 : name.Contains("cd") ? 2 : name.Contains("ef") ? 1 : 0
                 orderby order descending, item.FullName
                 select item;

score 0 · Answer 3 · answered Apr 12 '18 at 09:39

For custom ordering, you can assign a value to each compare condition and OrderByDescending will order by that. Something like this..

            lstModel = profileModel.Groups.OrderByDescending(m => m.FullName.ToLower().Contains("ab") ? 3 :
            m.FullName.ToLower().Contains("cd") ? 2 :
            m.FullName.ToLower().Contains("ef") ? 1 : 0).ToList();

score 0 · Answer 4 · answered Apr 12 '18 at 22:14

If you might have more or different level1 values to test, you may want a generic version.

Using a convenient extension method FirstOrDefault that takes the default value to return

public static T FirstOrDefault<T>(this IEnumerable<T> src, Func<T, bool> test, T defval) => src.Where(aT => test(aT)).DefaultIfEmpty(defval).First();

You can create an array of first level values in order, and sort first on that, then alphabetically:

var level1 = new[] { "ab", "cd", "ef" };

var ans = groups.OrderBy(i => level1.Select((op, n) => (op, n))
                                    .FirstOrDefault(opn => i.FullName.Contains(opn.op),
                                                    (op: String.Empty, n: level1.Length)).n)
                .ThenBy(i => i.FullName);

Order by multiple properties

4 Answers4