Faster TakeBy

Code:

public static IEnumerable<IEnumerable<T>> TakeBy<T>(this IEnumerable<T> source, int count)
{
    var grps = source.Select((val, i) => new { idx = i / count, val }).GroupBy(e => e.idx);
    return grps.Select(g => g.Select(e => e.val));
}