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

This is a general and IMHO elegant solution that will handle all cases correctly:

using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
    public static void Main()
    {
        IEnumerable r = Enumerable.Range(1, 20);
        foreach (int i in r.AllButLast(3))
            Console.WriteLine(i);

        Console.ReadKey();
    }
}

public static class LinqExt
{
    public static IEnumerable AllButLast(this IEnumerable enumerable, int n = 1)
    {
        using (IEnumerator enumerator = enumerable.GetEnumerator())
        {
            Queue queue = new Queue(n);

            for (int i = 0; i < n && enumerator.MoveNext(); i++)
                queue.Enqueue(enumerator.Current);

            while (enumerator.MoveNext())
            {
                queue.Enqueue(enumerator.Current);
                yield return queue.Dequeue();
            }
        }
    }
}