Question

I’ve this Collection for example:

1: A

2: B

3: A

4: C

5: A

6: C

I want to get the second repeated item from this collection in a LINQ query,

the required result is: 3:A, 6:C

Answer 1

A bit complicated but working:

int occ = 1; // 1 if you want the 2nd occurrence, 2 if you want the 3rd etc...
var nRepeatingElements = list.Select((x, idx) => new { Index = idx, Value = x })
                                .GroupBy(x => x.Value)
                                .Where(g => g.Count() > occ)
                                .Select(x => x.ElementAt(occ))
                                .ToList();

It returns a list with:

[Index:2 , Value: 'A']
[Index:5 , Value: 'C']

N.B.

The index is 1 lower than your desired solution, (because index is 0-based). But it’s really easy to increment it, even in the first LINQ Select if you want:

Select((x, idx) => new { Index = idx+1, Value = x })