Create batches in linq

Question

Can someone suggest a way to create batches of a certain size in linq?

Ideally I want to be able to perform operations in chunks of some configurable amount.

Answer 1

This is a fully lazy, low overhead, one-function implementation of Batch that doesn't do any accumulation. Based on (and fixes issues in) Nick Whaley's solution with help from EricRoller.

Iteration comes directly from the underlying IEnumerable, so elements must be enumerated in strict order, and accessed no more than once. If some elements aren't consumed in an inner loop, they are discarded (and trying to access them again via a saved iterator will throw InvalidOperationException: Enumeration already finished.).

You can test a complete sample at .NET Fiddle.

public static class BatchLinq
{
    public static IEnumerable> Batch(this IEnumerable source, int size)
    {
        if (size <= 0)
            throw new ArgumentOutOfRangeException("size", "Must be greater than zero.");
        using (var enumerator = source.GetEnumerator())
            while (enumerator.MoveNext())
            {
                int i = 0;
                // Batch is a local function closing over `i` and `enumerator` that
                // executes the inner batch enumeration
                IEnumerable Batch()
                {
                    do yield return enumerator.Current;
                    while (++i < size && enumerator.MoveNext());
                }

                yield return Batch();
                while (++i < size && enumerator.MoveNext()); // discard skipped items
            }
    }
}