C# Determine Duplicate in List [duplicate]

Answer 1

You could use Distinct() statement to find unique records. Then compare with original generic list like this:

  if (dgCoil.ItemsSource.Cast<BLL.Coil>().ToList().Count != dgCoil.ItemsSource.Cast<BLL.Coil>().Select(c => c.CoilNo).Distinct().Count())
  {    
    //Duplicate detected !!
    return;
  }

Answer 2

You can use IEnumerable.GroupBy method.

var list = new List<string> {"1", "2","3", "1", "2"};
var hasDuplicates = list.GroupBy(x => x).Any(x => x.Skip(1).Any());

Answer 3

Something along these lines is relatively simple and will provide you with a count of duplicates.

var something = new List<string>() { "One", "One", "Two", "Three" };

var dictionary = new Dictionary<string, int>();

something.ForEach(s =>
    {
        if (dictionary.ContainsKey(s))
        {
            dictionary[s]++;
        }
        else
        {
            dictionary[s] = 1;
        }
    });

I imagine this is similar to the implementation of Distinct, although I'm not certain.

Answer 4

You could use the Distinct() extension method for IEnumerable

Answer 5

If you are using integers or well ordered sets, use a binary tree for O(nlog n) performance.

Alternatively, find another faster means of sorting, then simply check that every value is different than the previous one.