remove contiguous duplicates in the sequence of objects [duplicate]

Question

suppose we have the list of objects

List<int> list = new List<int>() { 1,1,1,2,3,3,3,2,2,2,1,1 };

what is the most elegant way to get the following result list?

{1,2,3,2,1}

Answer 1

I like the idea of an extension method:

public static IEnumerable<T> RemoveContiguousDuplicates<T>(this IEnumerable<T> items) where T: IEquatable<T>
{
    bool init = false;
    T prev = default(T);

    foreach (T item in items)
    {
        if (!init)
            init = true;
        else if (prev.Equals(item))
            continue;

        prev = item;
        yield return item;
    }
}

And then, of course, to use it:

var singles = list.RemoveContiguousDuplicates().ToList();

Answer 2

Try this:

List<int> newList = new List<int>();
foreach (var item in list.Where(c => newList.Count == 0 || newList.Last() != c))
{
    newList.Add(item); // 1,2,3,2,1 will add to newList
}