C# extension method that can take an action that takes in a list.. so f(x) where x is a list, and break it up into batches of a certain size and do that action against each batch, either in serial or parallel.

batchextmethod.cs

  public static IEnumerable<T1> Batch<T,T1>(
            this IEnumerable<T> list, 
            int batchSize,  
            Func<IEnumerable<T>, IEnumerable<T1>>  action,
            bool processInParallel = false)
        {
            int i = 0;
            var grpqry = from item in list
                     group item by (int)i++ / batchSize
                         into part
                         select part.AsEnumerable();
            var prlqry = (processInParallel) ? grpqry.AsParallel() : grpqry;
            return prlqry.SelectMany(x => action(x)) ;
            
        }