Is this suitable for Linq GroupBy?

Question

I have a Dictionary :

      Dictionary<Project,List<User>> dictionary,

every Project has a group of Users.

I want to retrieve organize this data such that all the projects with similar users are arranged into this kind of data structure :

      List<Tuple<List<Project>,List<User>>>

I don't even know where to start. I've been fighting with this for days.

With similar users you mean projects having the same users in their subcollection? — Jeroen, Aug 03 '11 at 03:33
yes, that's what I mean. Projects that have the same users in heir subcollection. — Attilah, Aug 03 '11 at 03:36

score 0 · Answer 1 · answered Aug 03 '11 at 03:35

0

Your best best would be to flatten the contents of dictionary and query against that.

answered Aug 03 '11 at 03:35

Babak Naffas

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score 0 · Accepted Answer · answered Aug 03 '11 at 08:13

0

The lists of users are the key by which you should group. In the GroupBy() you could use a comparer like this one:

public class ListComparer<T> : IEqualityComparer<List<T>>
    where T : IComparable<T>
{
    public bool Equals(List<T> x, List<T> y)
    {
        return x.OrderBy(u => u).SequenceEqual(y.OrderBy(u => u));
    }

    public int GetHashCode(List<T> obj)
    {
        return obj.GetHashCode();
    }
}

BTW: The comparer is on Lists and not on IEnumerables, otherwise for each comparison the compared objects should be enumerated over and over.

answered Aug 03 '11 at 08:13

Gert Arnold

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You might want to follow [this thread](http://stackoverflow.com/questions/6948019/linq-implementation-of-cartesian-product-with-pruning) for a more robust comparer. – Gert Arnold Aug 04 '11 at 21:45
I'd like to delete this answer because it's not good. But it's accepted so it can't be deleted. The GetHashCode method doesn't make sense. It should match the `Equals` method but it doesn't. – Gert Arnold Feb 22 '21 at 07:17

Is this suitable for Linq GroupBy?

2 Answers2