我有以下列表:
RakeSnapshots、ProductMovements
目的是对两者进行处理,得到符合条件的元素的个数,如下:
考虑
RakeSnapshots
和StatusCode == "Dumping"
考虑
ProductMovement
和Status == "InProgress"
- 获取两个列表中所有元素的
count
,满足条件RakeSnapshots.RakeCode
等于ProductMovements.ProductCode
以下是我目前的选择:
//代码 1:
var resultCount = ProductMovements.Where(x => RakeSnapshots
.Where(r => r.StatusCode == "Dumping")
.Any(y => y.RakeCode == x.ProductCode &&
x.Status == "InProgress"))
.Count();
//代码 2:
var productMovementsInprogress = ProductMovements.Where(x => x.Status == "InProgress");
var rakeSnapShotsDumping = RakeSnapshots.Where(r => r.StatusCode == "Dumping");
var resultCount = productMovementsInprogress.Zip(rakeSnapShotsDumping,(x,y) => (y.RakeCode == x.ProductCode) ? true : false)
.Where(x => x).Count();
挑战是这两个代码都是O(n^2)
复杂度,有没有办法改进它,如果数据非常大,这会造成伤害
最佳答案
您可以使用 inner join
这样做:
var dumpingRakeSnapshots = rakeSnapshots.Where(r => r.StatusCode == "Dumping");
var inProgressProductMovements = productMovements.Where(p => p.Status == "InProgress");
var matches =
from r in dumpingRakeSnapshots
join p in inProgressProductMovements on r.RakeCode equals p.ProductCode
select r;
int count = matches.Count(); // Here's the answer.
请注意(正如 Ivan Stoev 指出的那样)这仅在 RakeCode 是 RakeSnapshots
的主键时有效。
如果不是,则必须使用 grouped join
.
这是您在这种情况下应该使用的 Linq 查询语法版本,但请注意,这与 Ivan 的回答完全相同(仅在 Linq 查询形式中):
var matches =
from r in dumpingRakeSnapshots
join p in inProgressProductMovements on r.RakeCode equals p.ProductCode into gj
select gj;
为了完整起见,这里有一个可编译的控制台应用程序,它演示了如果 RakeCode
和 ProductCode
不是主键,您将获得的不同结果:
using System;
using System.Collections.Generic;
using System.Linq;
namespace ConsoleApp1
{
class RakeSnapshot
{
public string StatusCode;
public string RakeCode;
}
class ProductMovement
{
public string Status;
public string ProductCode;
}
sealed class Program
{
void run()
{
var rakeSnapshots = new List<RakeSnapshot>
{
new RakeSnapshot {StatusCode = "Dumping", RakeCode = "1"},
new RakeSnapshot {StatusCode = "Dumping", RakeCode = "1"},
new RakeSnapshot {StatusCode = "Dumping", RakeCode = "2"}
};
var productMovements = new List<ProductMovement>
{
new ProductMovement {Status = "InProgress", ProductCode = "1"},
new ProductMovement {Status = "InProgress", ProductCode = "2"},
new ProductMovement {Status = "InProgress", ProductCode = "2"}
};
var dumpingRakeSnapshots = rakeSnapshots.Where(r => r.StatusCode == "Dumping");
var inProgressProductMovements = productMovements.Where(p => p.Status == "InProgress");
// Inner join.
var matches1 =
from r in dumpingRakeSnapshots
join p in inProgressProductMovements on r.RakeCode equals p.ProductCode
select r;
Console.WriteLine(matches1.Count());
// Grouped join.
var matches2 =
from r in dumpingRakeSnapshots
join p in inProgressProductMovements on r.RakeCode equals p.ProductCode into gj
select gj;
Console.WriteLine(matches2.Count());
// OP's code.
var resultCount =
productMovements
.Count(x => rakeSnapshots
.Where(r => r.StatusCode == "Dumping")
.Any(y => y.RakeCode == x.ProductCode && x.Status == "InProgress"));
Console.WriteLine(resultCount);
}
static void Main(string[] args)
{
new Program().run();
}
}
}
关于c# - 提高当前 Linq 查询的时间复杂度,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/39117516/