这是我的第四篇文章（感谢@tanascius将其推进到更多的LINQ中）：
public static IEnumerable<T> MergePreserveOrder3<T, TOrder>( this IEnumerable<IEnumerable<T>> aa, Func<T, TOrder> orderFunc)where TOrder : IComparable<TOrder>{ var items = aa.Select(xx => xx.GetEnumerator()).Where(ee => ee.MoveNext()) .OrderBy(ee => orderFunc(ee.Current)).ToList(); while (items.Count > 0) { yield return items[0].Current; var next = items[0]; items.RemoveAt(0); if (next.MoveNext()) { // simple sorted linear insert var value = orderFunc(next.Current); var ii = 0; for ( ; ii < items.Count; ++ii) { if (value.CompareTo(orderFunc(items[ii].Current)) <= 0) { items.Insert(ii, next); break; } } if (ii == items.Count) items.Add(next); } else next.Dispose(); // woops! can't forget IDisposable }}结果：
for (int p = 0; p < people.Count; ++p){ Console.WriteLine("List {0}:", p + 1); Console.WriteLine("t{0}", String.Join(", ", people[p].Select(x => x.Name)));}Console.WriteLine("Merged:");foreach (var person in people.MergePreserveOrder(pp => pp.Age)){ Console.WriteLine("t{0}", person.Name);}List 1: 8yo, 22yo, 47yo, 49yoList 2: 35yo, 47yo, 60yoList 3: 28yo, 55yo, 64yoMerged: 8yo 22yo 28yo 35yo 47yo 47yo 49yo 55yo 60yo 64yo通过.Net 4.0的Tuple支持进行了改进：
public static IEnumerable<T> MergePreserveOrder4<T, TOrder>( this IEnumerable<IEnumerable<T>> aa, Func<T, TOrder> orderFunc) where TOrder : IComparable<TOrder>{ var items = aa.Select(xx => xx.GetEnumerator()) .Where(ee => ee.MoveNext()) .Select(ee => Tuple.Create(orderFunc(ee.Current), ee)) .OrderBy(ee => ee.Item1).ToList(); while (items.Count > 0) { yield return items[0].Item2.Current; var next = items[0]; items.RemoveAt(0); if (next.Item2.MoveNext()) { var value = orderFunc(next.Item2.Current); var ii = 0; for (; ii < items.Count; ++ii) { if (value.CompareTo(items[ii].Item1) <= 0) { // NB: using a tuple to minimize calls to orderFunc items.Insert(ii, Tuple.Create(value, next.Item2)); break; } } if (ii == items.Count) items.Add(Tuple.Create(value, next.Item2)); } else next.Item2.Dispose(); // woops! can't forget IDisposable }}
