如何优化linq查询以按价格对日期进行分组而不合并结果

问题描述

我有这个linq查询如下所述。问题是当数据按价格分组时，它将按日期分组，而不考虑非连续日期可能出现相同价格的情况。 c>使用系统;
使用System.Collections.Generic;
使用System.Linq;

public class Program
{
public static void Main（）
{
//Console.WriteLine(\"Hello World）;
列表<价格> list = new List< Prices>（）;
list.Add（new Prices（）{Date = DateTime.Parse（2017-06-17），Price = Double.Parse（50）}）;
list.Add（new Prices（）{Date = DateTime.Parse（2017-06-18），Price = Double.Parse（50）}）;
list.Add（new Prices（）{Date = DateTime.Parse（2017-06-19），Price = Double.Parse（50）}）;
list.Add（new Prices（）{Date = DateTime.Parse（2017-06-20），Price = Double.Parse（100）}）;
list.Add（new Prices（）{Date = DateTime.Parse（2017-06-21），Price = Double.Parse（100）}）;
list.Add（new Prices（）{Date = DateTime.Parse（2017-06-22），Price = Double.Parse（100）}）;
list.Add（new Prices（）{Date = DateTime.Parse（2017-06-23），Price = Double.Parse（50）}）;
list.Add（new Prices（）{Date = DateTime.Parse（2017-06-24），Price = Double.Parse（50）}）;
list.Add（new Prices（）{Date = DateTime.Parse（2017-06-25），Price = Double.Parse（50）}）;


var baseservices = list
.GroupBy（l => l.Price）
.Select（g => new
{
Price = g.Key，
PeriodStart = g.Select（l => l.Date）.Min（），
PeriodEnd = g.Select（l => l.Date）。 Max（），
}）;

foreach（baseservices中的var item）
{
Console.WriteLine（item.Price ++ item.PeriodStart ++ item.PeriodEnd）;




$ b公共类价格
{
public DateTime Date {get; set;}
public double Price {get; set;}
}

public class Quote
{
public DateTime PeriodStart {get; set;}
public DateTime PeriodEnd {get; set;}
public double Price {get; set;}
}

结果是

  50 2017/5/17 12:00:00 AM 6/25/2017 ：00：00 AM 
 100 6/20/2017 12:00:00 AM 6/22/2017 12:00:00 AM 
  

我如何得到以下结果：

  50 6/17/2017 12： 00:00 AM 6/29/2017 12:00:00 AM 
 100 6/20/2017 12:00:00 6/22/2017 12:00:00 AM 
 50 6/23 / 2017 12:00:00 AM 6/25/2017 12:00:00 AM 
  

解决方案

LINQ不适合这样的操作。唯一可用于执行此类处理的标准LINQ操作符是，但它不超过LINQ-ish foreach 循环：

  var baseservices = list 
 .OrderBy（e => e.Date）
。如果（r.Count> 0& r [r.Count-1] .Price = 1，则集合（新列表< Quote> = e.Price&& r [r.Count  -  1] .PeriodEnd.AddDays（1）== e.Date）
r [r.Count  -  1] .PeriodEnd = e.Date; 
 else 
 r.Add（新报价{Price = e.Price，PeriodStart = e.Date，PeriodEnd = e.Date}）; 
 return r; 
}）; 
  

请注意，与许多LINQ方法相反，它会立即执行并且不会返回，直到整个结果为止准备好。

I have this linq query as stated below. The problem is when the data is grouped by price, it groups dates by price without considering a case where same price can occur for nonconsecutive dates

using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
    public static void Main()
    {
        //Console.WriteLine("Hello World");
        List<Prices> list = new List<Prices>();
        list.Add(new Prices() { Date = DateTime.Parse("2017-06-17"), Price = Double.Parse("50")});
        list.Add(new Prices() { Date = DateTime.Parse("2017-06-18"), Price = Double.Parse("50")});
        list.Add(new Prices() { Date = DateTime.Parse("2017-06-19"), Price = Double.Parse("50")});
        list.Add(new Prices() { Date = DateTime.Parse("2017-06-20"), Price = Double.Parse("100")});
        list.Add(new Prices() { Date = DateTime.Parse("2017-06-21"), Price = Double.Parse("100")});
        list.Add(new Prices() { Date = DateTime.Parse("2017-06-22"), Price = Double.Parse("100")});
        list.Add(new Prices() { Date = DateTime.Parse("2017-06-23"), Price = Double.Parse("50")});
        list.Add(new Prices() { Date = DateTime.Parse("2017-06-24"), Price = Double.Parse("50")});
        list.Add(new Prices() { Date = DateTime.Parse("2017-06-25"), Price = Double.Parse("50")});


        var baseservices = list
                .GroupBy(l => l.Price)
                .Select(g => new
                {
                    Price = g.Key,
                    PeriodStart = g.Select(l=>l.Date).Min(),
                    PeriodEnd = g.Select(l => l.Date).Max(),
                });

        foreach(var item in baseservices)
        {
            Console.WriteLine(item.Price + " " + item.PeriodStart + " " + item.PeriodEnd);
        }

    }
}

public class Prices
{
    public DateTime Date {get;set;}
    public double Price {get;set;}
}

public class Quote
{
    public DateTime PeriodStart {get;set;}
    public DateTime PeriodEnd {get;set;}
    public double Price {get;set;}
}

The result is

50 6/17/2017 12:00:00 AM 6/25/2017 12:00:00 AM
100 6/20/2017 12:00:00 AM 6/22/2017 12:00:00 AM

How can I get the following result

50 6/17/2017 12:00:00 AM 6/29/2017 12:00:00 AM
100 6/20/2017 12:00:00 AM 6/22/2017 12:00:00 AM
50 6/23/2017 12:00:00 AM 6/25/2017 12:00:00 AM

解决方案

LINQ is not well suited for such operations. The only standard LINQ operator that can be used to do such processing is Aggregate, but it's no more than LINQ-ish foreach loop:

var baseservices = list
    .OrderBy(e => e.Date)
    .Aggregate(new List<Quote>(), (r, e) =>
    {
        if (r.Count > 0 && r[r.Count - 1].Price == e.Price && r[r.Count - 1].PeriodEnd.AddDays(1) == e.Date)
            r[r.Count - 1].PeriodEnd = e.Date;
        else
            r.Add(new Quote { Price = e.Price, PeriodStart = e.Date, PeriodEnd = e.Date });
        return r;
    });

Note that in contrast with many LINQ methods, this executes immediate and does not return until the whole result is ready.

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