Sort an array of objects according to another array of objects in C#

Question

I have two objects. I want to sort first object's QuickLinks property according to second object's QuickLinks. It should be based on QuickLinkContent.ConfigId

NavigationMenuContent nmc1 = new NavigationMenuContent();
NavigationMenuContent nmc2 = new NavigationMenuContent();

public class NavigationMenuContent
    {
        public int LanguageID { get; set; }

        public QuickLinkContent[] QuickLinks { get; set; }
    }

public class QuickLinkContent
    {
        public Guid ConfigID { get; set; }

        public string Name { get; set; }

        public string Description { get; set; }

        public string Url { get; set; }

        public Guid? ServiceProviderID { get; set; }

        public SchemeContentFile Document { get; set; }
    }

I tried doing it like this:

nmc1.QuickLinks = nmc1.QuickLinks.OrderBy(q => nmc2.QuickLinks.ToList().IndexOf(q.ConfigID));

but getting error :

Cannot convert from System.Guid to QuickLnkContent.

You say you want to sort `nmc1` list, but you are trying to sort `QuickLinks` array. So what you are actually trying to sort? — Sergey Berezovskiy, Jan 13 '21 at 20:39
What does that even mean? For example, if I said "I want to sort this Person[] according to FirstName alphabetical descending" - that makes sense.. but "I want to sort this Person[] according to that Person[]" - it's not a specification of anything — Caius Jard, Jan 13 '21 at 20:40
@SergeyBerezovskiy sorry for confustion, I've updated the question — Prashant Yadav, Jan 13 '21 at 20:46
Types are always your friend in C#: what is the type of `q.ConfigID`? What is the type of `nmc2.QuickLinks`? How do you expect `IndexOf` to work? — NetMage, Jan 13 '21 at 20:54
Do the `QuickLinkContent[] QuickLinks` arrays contain the same `Guid ConfigID`, just in a different order? What if there are missing items; do the missing elements get sorted to the end of the list? — Enigmativity, Jan 13 '21 at 21:09
@Enigmativity yes, it contains same configId. There won't be missing items — Prashant Yadav, Jan 13 '21 at 21:13

score 3 · Answer 1 · answered Jan 13 '21 at 21:13

3

I would use a dictionary to do this.

Dictionary<Guid, int> map =
    nmc2
        .QuickLinks
        .Select((x, n) => (x, n))
        .ToDictionary(z => z.x.ConfigID, z => z.n);

nmc1.QuickLinks =
    nmc1
        .QuickLinks
        .OrderBy(x => map[x.ConfigID])
        .ToArray();

answered Jan 13 '21 at 21:13

Enigmativity

113,464
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This is the faster method usually – Charlieface Jan 13 '21 at 21:20

score 1 · Accepted Answer · answered Jan 13 '21 at 20:56

1

Create array of ordered config ids:

var orderedIds = nmc2.QuickLinks.Select(ql => ql.ConfigID).ToArray();

And then use it to order links

nmc1.QuickLinks = nmc1.QuickLinks
   .OrderBy(ql => Array.IndexOf(orderedIds, ql.ConfigID))
   .ToArray();

answered Jan 13 '21 at 20:56

Sergey Berezovskiy

232,247
41
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459

O(n2) operation. The other solution will usually be faster – Charlieface Jan 13 '21 at 21:20
@Charlieface first of all it's premature optimization. You don't want to create dictionaries to sort an array of 5 items. And other solution will fail 1) when nmc1 has unique items, 2) when nmc2 has duplicates. So you (maybe) saved few ticks of cpu, but got more code to maintain and two problems to deal with – Sergey Berezovskiy Jan 13 '21 at 22:06

score 1 · Answer 3 · answered Jan 13 '21 at 21:44

Using an array extension method, you can solve this generally:

public static int IndexOfBy<T, TKey>(this T[] a, TKey target, Func<T,TKey> keyFn, EqualityComparer<TKey> cmp = null) {
    cmp = cmp ?? EqualityComparer<TKey>.Default;
    for (int j1 = 0; j1 < a.Length; ++j1) {
        if (cmp.Equals(keyFn(a[j1]), target))
            return j1;
    }
    return -1;
}

With the extension method available, you can use OrderBy:

nmc1.QuickLinks = nmc2.QuickLinks.OrderBy(q => nmc2.QuickLinks.IndexOfBy(q.ConfigID, q2 => q2.ConfigID)).ToArray();

Sort an array of objects according to another array of objects in C#

3 Answers3