private static Task[] GenerateTasks(IPostingLineCollection postingLineCollection, Predicate <IPostingLine> selector, Func <IReadOnlyCollection <IPostingLine>, Task> taskGenerator)
{
NullGuard.NotNull(postingLineCollection, nameof(postingLineCollection))
.NotNull(selector, nameof(selector))
.NotNull(taskGenerator, nameof(taskGenerator));
return(postingLineCollection.AsParallel()
.GroupBy(postingLine => postingLine.PostingDate.Year)
.Select(group => taskGenerator(group.AsParallel().Where(postingLine => selector(postingLine)).ToArray()))
.ToArray());
}