调试易

        public struct Unit
        {
            public List<Business> list;
            public float Subtotal;
        }        public struct Business
        {
            public string ID;
            public string Currency;
            public float Amount;
        }        public static IEnumerable<Unit> GetUnits()
        {
            var dataSource = new List<Business>();
            var result = new Dictionary<KeyValuePair<string, string>, Unit>();
            foreach (var b in dataSource)
            {
                var key = new KeyValuePair<string, string>(b.ID, b.Currency);
                if(!result.Keys.Contains(key))
                {
                    var unit = new Unit();
                    unit.list.Add(b);
                    unit.Subtotal += b.Amount;
                    result.Add(key, unit);
                }
                else
                {
                    var unit = result[key];
                    unit.list.Add(b);
                    unit.Subtotal += b.Amount;
                }
            }
            return result.Values;
        }
直接遍历就是了，如果一定要用linq,就只能添加一个字段用来区分小结行和原始数据行，看你数据量多大了，优化的空间还是有的。

你还是要LINQ直接查出来？那就加字段把小结行区分出来，我给你弄一下，效率未必比这个高

        public struct Business
        {
            public string ID;
            public string Currency;
            public float Amount;
            public bool IsSubtotal;
        }        public static IEnumerable<Business> GetUnits()
        {
            var dataSource = new List<Business>();
            var test = from b in dataSource
                       group b by new {b.ID, b.Currency}
                       into g
                       select 
                       new Business
                       {
                           ID = g.Key.ID,
                           Currency = g.Key.Currency,
                           Amount = g.Sum(i => i.Amount),
                           IsSubtotal = true
                       };
            dataSource.AddRange(test.ToList());
            dataSource.OrderBy(i => new {i.ID, i.Currency});
            return dataSource;
        }
步骤1：手动修改Business类，加上一个字段，IsSubtotal
步骤2：查出小计再与源数据合并
步骤3：界面层根据IsSubtotal的值决定是否显示编号和币种。