Check List for duplications with optional words to exclude

Question

I have a method as below. Method return either false/true either when list contains duplicates or not. I would like to extend my method to say for instance (optional) that i

Answer 1

Instead of making your method more complicated, you should open it more to combine it with others:

public static class MyLinqMethods
{
  public static bool HasDuplicates<T>(this IEnumerable<T> sequence)
  {
      return sequence.GroupBy(n => n).Any(c => c.Count() > 1);
  }
}

Now you can use it with Linq:

var original = new[] { string.Empty, "Hello", "World", string.Empty };

var duplicatesInOriginal = original.HasDuplicates();

var duplicatesIfStringEmptyIsIgnored = original.Where(o => o != string.Empty).HasDuplicates();

Answer 2

This will also help, using a 'params' in arguments and then doing Except()

  public static bool IsListContainsDuplicates<T>(List<T> list, params T[] optional)
        {
            return list.Except(optional).GroupBy(n => n).Any(c => c.Count() > 1);
        }

You can call like this if you doesn't want to exclude anything:

IsListContainsDuplicates(list)

Else, just pass the params values, for example, if the list is an integer list then,

IsListContainsDuplicates(list,5,4)

Answer 3

You can use Except(). From MSDN:

Produces the set difference of two sequences by using the default equality comparer to compare values.

return list.Except(listToExclude).GroupBy(n => n).Any(c => c.Count() > 1);

Answer 4

public static bool ContainsDuplicates<T>(this IEnumerable<T> items, IEnumerable<T> itemsToExclude = null)
{
    if (itemsToExclude == null) itemsToExclude = Enumerable.Empty<T>();
    return items.Except(itemsToExclude)
                .GroupBy(n => n)
                .Any(c => c.Count() > 1);
}

But i'd prefer this implementation because it's more performant:

public static bool ContainsDuplicates<T>(this IEnumerable<T> items, IEnumerable<T> itemsToExclude = null)
{
    if (itemsToExclude == null) itemsToExclude = Enumerable.Empty<T>();
    HashSet<T> set = new HashSet<T>();
    return !items.Except(itemsToExclude).All(set.Add);
}