Question

我找不到具体的例子，所以发帖提问。任何帮助表示赞赏。

我有两个大型通用列表，都有超过300K的项目。

我循环浏览第一个列表以回读信息并动态生成新列表的新项目，但我需要在第二个列表中搜索并根据三个匹配条件返回一个值（如果找到）添加到列表中，但是你可以想象，这样做300k * 300k次需要时间。

有什么方法可以更有效地做到这一点吗？

我的代码：

var reportList = new List<StocksHeldInCustody>();
foreach (var correctDepotHolding in correctDepotHoldings)
  {
    var reportLine = new StocksHeldInCustody();
    reportLine.ClientNo = correctDepotHolding.ClientNo;
    reportLine.Value = correctDepotHolding.ValueOfStock;
    reportLine.Depot = correctDepotHolding.Depot;
    reportLine.SEDOL = correctDepotHolding.StockCode;
    reportLine.Units = correctDepotHolding.QuantityHeld;
    reportLine.Custodian = "Unknown";
    reportLine.StockName = correctDepotHolding.StockR1.Trim() + " " + correctDepotHolding.StockR2.Trim();

    //Get custodian info

    foreach (var ccHolding in ccHoldList)
    {
      if (correctDepotHolding.ClientNo != ccHolding.ClientNo) continue;
      if (correctDepotHolding.Depot != ccHolding.Depot) continue;
      if (correctDepotHolding.StockCode != ccHolding.StockCode) continue;
      if (correctDepotHolding.QuantityHeld != ccHolding.QuantityHeld) continue;
      reportLine.Custodian = ccHolding.Custodian;
      break;
    }
    reportList.Add(reportLine);
  }

Answer 1

正如Pranay所说，加入可能是你想要的：

var query = from correct in correctDepotHoldings
            join ccHolding in ccHoldList
              on new { correct.ClientNo, correct.Depot,
                       correct.StockCode, correct.QuantityHeld }
              equals new { ccHolding.ClientNo, ccHolding.Depot,
                           ccHolding.StockCode, ccHolding.QuantityHeld }
            // TODO: Fill in the properties here based on correct and ccHolding
            select new StocksHeldInCustody { ... };
var reportList = query.ToList();

Answer 2

您可以将数据从查找列表移动到字典中，其中键是您要搜索的3个项目的唯一哈希值。然后，您将拥有非常快速的查找并节省数百万次迭代。

Answer 3

查看我的完整帖子：Linq Join on Mutiple columns using Anonymous type

利用Linq内部联接，它将为您效劳。

var list =  ( from x in entity
           join y in entity2 
          on new { x.field1, x.field2 } 
        equals new { y.field1, y.field2 }
        select new entity { fields to select}).ToList();

linq加入多个领域

enter image description here

EmployeeDataContext edb= new EmployeeDataContext();
var cust = from c in edb.Customers
           join d in edb.Distributors on
             new { CityID = c.CityId, StateID = c.StateId, CountryID = c.CountryId,
                   Id = c.DistributorId }   
           equals
             new { CityID = d.CityId, StateID = d.StateId, CountryID = d.CountryId,
                   Id = d.DistributorId }   
           select c;

Answer 4

使用LINQ加入列表并按照您的喜好返回。

例如

var list1 = GetMassiveList();
var list2 = GetMassiveList();

var list3 = from a in list1
            join b in list2
                 on new { a.Prop1, a.Prop2 } equals
                    new { b.Prop1, b.Prop2 } 
            select new { a.Prop1, b.Prop2 };

要进行外部联接，可以使用DefaultIfEmpty（）此示例将连接的RIGHT部分设置为默认对象（通常为null），用于未进行连接的情况。

例如

from a in list1
join b in list2
    on new { a.Prop1, a.Prop2 } equals
       new { b.Prop1, b.Prop2 } 
into outer
from b in outer.DefaultIfEmpty()
select new 
    Prop1 = a.Prop1,
    Prop2 = b != null ? b.Prop2 : "Value for Prop2 if the b join is null"
}

比较两个大型通用列表

4 个答案: