Get Non-Distinct elements from an IEnumerable

Question

I have a class called Item. Item has an identifier property called ItemCode which is a string. I would like to get a list of all non-distinct Items in a list of Items.

E

Answer 1

I'd suggest writing a custom extension method, something like this:

static class RepeatedExtension
{
    public static IEnumerable Repeated(this IEnumerable source)
    {
        var distinct = new Dictionary();
        foreach (var item in source)
        {
            if (!distinct.ContainsKey(item))
                distinct.Add(item, 1);
            else
            {
                if (distinct[item]++ == 1) // only yield items on first repeated occurence
                    yield return item;
            }                    
        }
    }
}

You also need to override Equals() method for your Item class, so that items are correctly compared by their code.