How to Efficiently Get the Last N Elements of a Collection Using LINQ?

How to Retrieve the Last N Elements of a Collection Using LINQ

To obtain the last N elements of a collection, LINQ offers the efficient Skip() method. By combining it with a conditional statement via Math.Max(), we can avoid errors stemming from negative input.

collection.Skip(Math.Max(0, collection.Count() - N));

This approach preserves the original item order without resorting to sorting and is compatible with multiple LINQ providers.

For more flexibility, the provided extension method encapsulates the above logic:

public static class MiscExtensions
{
    public static IEnumerable<T> TakeLast<T>(this IEnumerable<T> source, int N)
    {
        return source.Skip(Math.Max(0, source.Count() - N));
    }
}

Usage:

collection.TakeLast(5);

While the Count() call incurs an enumeration for certain data structures, optimizations exist for common ones like Lists and Arrays. For forward-only enumerables, alternative one-pass algorithms (e.g., by Lasse V. Karlsen or Mark Byers) avoid multiple passes over the data.

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