Question

I have a single array with these entries:

{1, 1, 2, 2, 3,3,3, 4}

and i want to transform them to ( 3 lists in this case ):

{1,2,3,4}
{1,2,3}
{3}

Is there any way to do this with LINQ or SQL? I guess there’s a mathematical term for this operation, which I don’t know unfortunately…

Or do I have to do it with loops?

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EDIT: I can’t really describe the logic, so here are more examples.. It more or less loops multiple times over the array and takes every number once ( but every number only once per round ) until there are no numbers left

{1, 1, 2, 2, 3,3,3, 4, 5}
would be
{1,2,3,4,5}
{1,2,3}
{3}

or

{1, 1, 2, 2,2, 3,3,3, 4, 5}
would be
{1,2,3,4,5}
{1,2,3}
{2,3}

Answer 1

private IEnumerable<List<int>> FooSplit(IEnumerable<int> items)
{
    List<int> source = new List<int>(items);
    while (source.Any())
    {
        var result = source.Distinct().ToList();
        yield return result;
        result.ForEach(item => source.Remove(item));
    }
}

Usage:

int[] items =  { 1, 1, 2, 2, 3, 3, 3, 4 };

foreach(var subList in FooSplit(items))
{
    // here you have your three sublists
}

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Here is another solution, which is less readable but it will have better performance:

private IEnumerable<IEnumerable<int>> FooSplit(IEnumerable<int> items)
{
    var groups = items.GroupBy(i => i).Select(g => g.ToList()).ToList();    

    while (groups.Count > 0)
    {
       yield return groups.Select( g => 
             { var i = g[0]; g.RemoveAt(g.Count - 1); return i; });
       groups.RemoveAll(g => g.Count == 0);
    }
}