How to take all but the last element in a sequence using LINQ?

Question

Let\'s say I have a sequence.

IEnumerable sequence = GetSequenceFromExpensiveSource();
// sequence now contains: 0,1,2,3,...,999999,1000000
         


        

Answer 1

A slight expansion on Joren's elegant solution:

public static IEnumerable Shrink(this IEnumerable source, int left, int right)
{
    int i = 0;
    var buffer = new Queue(right + 1);

    foreach (T x in source)
    {
        if (i >= left) // Read past left many elements at the start
        {
            buffer.Enqueue(x);
            if (buffer.Count > right) // Build a buffer to drop right many elements at the end
                yield return buffer.Dequeue();    
        } 
        else i++;
    }
}
public static IEnumerable WithoutLast(this IEnumerable source, int n = 1)
{
    return source.Shrink(0, n);
}
public static IEnumerable WithoutFirst(this IEnumerable source, int n = 1)
{
    return source.Shrink(n, 0);
}

Where shrink implements a simple count forward to drop the first left many elements and the same discarded buffer to drop the last right many elements.