获取数量缺货的日期

Question

尝试使用 LINQ C# 找出当数量缺货时如何获得日期范围结果

假设我有一个看起来像这样的表格结果

EventDate  | Qty
2014-02-03 | 6
2014-02-04 | -1
2014-02-05 | -2
2014-02-06 | 2
2014-02-07 | -1
2014-02-08 | -2
2014-02-09 | -3
2014-02-10 | 5

现在我想像这样获得库存数量为负0时的日期范围

FromDate   | ToDate
2014-02-04 | 2014-02-05
2014-02-07 | 2014-02-09

有人可以帮助我如何实现吗？

更新

我知道我可以通过乘以查询来做到这一点，但如果可能的话，我想只在一个 LINQ 查询中做到这一点。

Answer 1

对于仅使用内置函数的替代方法，

这里的策略是选择数量小于零的所有日期，并为每个日期执行一个子查询，该子查询构建一个包含当前日期之后数量也小于零的所有日期的列表。使用TakeWhile，这将在下一个日期之前以非负数停止。然后取其中的最大值，这对于范围的结束日期是正确的。最后一步是 GroupBy 删除映射到同一结束日期的“缺货”范围开始后的所有天数，从而为您提供不同的缺货日期范围。

如下所示，它依赖于输入时按时间顺序排序的库存水平。

public class StockLevel
{
    public DateTime Date { get; set; }
    public int Quantity { get; set; }                        
}

static void Main(string[] args)
{
    List<StockLevel> stockLevels = new List<StockLevel>()
    { 
        new StockLevel() { Date = DateTime.Parse("03-Feb-2014"), Quantity = 6 },
        new StockLevel() { Date = DateTime.Parse("04-Feb-2014"), Quantity = -1 },
        new StockLevel() { Date = DateTime.Parse("05-Feb-2014"), Quantity = -2 },
        new StockLevel() { Date = DateTime.Parse("06-Feb-2014"), Quantity = 2 },
        new StockLevel() { Date = DateTime.Parse("07-Feb-2014"), Quantity = -1 },
        new StockLevel() { Date = DateTime.Parse("08-Feb-2014"), Quantity = -2 },
        new StockLevel() { Date = DateTime.Parse("09-Feb-2014"), Quantity = -3 },
        new StockLevel() { Date = DateTime.Parse("10-Feb-2014"), Quantity = 5 },
    };

    var outOfStockDates = stockLevels
        .Where(a => a.Quantity < 0)
        .Select(a => new 
        { 
                S1 = a.Date, 
                S2 = stockLevels
                        .Where(c => c.Date >= a.Date)
                        .TakeWhile(b => b.Quantity < 0)
                        .Select(b => b.Date).Max() 
        })
        .GroupBy(a => a.S2, a => a.S1, (S2, S1S) => new { FromDate = S1S.Min(), ToDate = S2 });

    Console.ReadKey();
}

Answer 2

您可以编写自己的自定义函数来更改为 Linq 表达式。

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

namespace ConsoleApplication
    {
    public class Class1
        {
        public static void Main(string[] args)
            {
            IEnumerable<QuantityDate> quantityDates = GetQuantityDates();//I'm sure you already have some way of retrieving these, via EF or Linq to SQL etc.
            var results = quantityDates.Where(qd => qd.Qty < 0).CombineResults(); //This is the main Linq expression
            foreach (var result in results)
                {
                Console.WriteLine("From Date: {0} To Date: {1}", result.FromDate, result.ToDate);
                }
            Console.WriteLine("Press any key to exit.");
            Console.ReadKey();
            }

        //Just to see the data for the moment. You'll probably get this data via EF or Linq to SQL
        public static List<QuantityDate> GetQuantityDates()
            {
            List<QuantityDate> seed = new List<QuantityDate>()
            {
            new QuantityDate() { EventDate = new DateTime(2014, 2, 3), Qty = 6 },
            new QuantityDate() { EventDate = new DateTime(2014, 2, 4), Qty = -1 },
            new QuantityDate() { EventDate = new DateTime(2014, 2, 5), Qty = -2 },
            new QuantityDate() { EventDate = new DateTime(2014, 2, 6), Qty = 2 },
            new QuantityDate() { EventDate = new DateTime(2014, 2, 7), Qty = -1 },
            new QuantityDate() { EventDate = new DateTime(2014, 2, 8), Qty = -2 },
            new QuantityDate() { EventDate = new DateTime(2014, 2, 9), Qty = -3 },
            new QuantityDate() { EventDate = new DateTime(2014, 2, 10), Qty = 5 }
            };
            return seed;
            }
        }
    public static class Extensions
        {

        //This is where the magic happens, and we combine the results
        public static List<OutOfStockRange> CombineResults(this IEnumerable<QuantityDate> input)
            {
            List<OutOfStockRange> output=new List<OutOfStockRange>();
            OutOfStockRange lastEntered = null;
            foreach(var qd in input.OrderBy(qd => qd.EventDate))
             {
                 if(lastEntered != null && lastEntered.ToDate.AddDays(1) == qd.EventDate)
                 {
                     lastEntered.ToDate = qd.EventDate;
                 }
                 else
                 {
                     lastEntered =new OutOfStockRange(){FromDate = qd.EventDate, ToDate = qd.EventDate};
                     output.Add(lastEntered);
                 }
            }
            return output;
        }
        }

    //This class represents the input data
    public class QuantityDate
        {
        public DateTime EventDate { get; set; }
        public int Qty { get; set; }
        }

    //This class represents the output data
    public class OutOfStockRange
        {
        public DateTime FromDate { get; set; }
        public DateTime ToDate { get; set; }
        }
    }

Answer 3

我会这样做。

从您的数据开始：

var stockQuantities = new []
{
    new { Date = new DateTime(2014, 2, 3), Qty = 6 },
    new { Date = new DateTime(2014, 2, 4), Qty = -1 },
    new { Date = new DateTime(2014, 2, 5), Qty = -2 },
    new { Date = new DateTime(2014, 2, 6), Qty = 2 },
    new { Date = new DateTime(2014, 2, 7), Qty = -1 },
    new { Date = new DateTime(2014, 2, 8), Qty = -2 },
    new { Date = new DateTime(2014, 2, 9), Qty = -3 },
    new { Date = new DateTime(2014, 2, 10), Qty = 5 },
};

然后查询缺货记录：

var outOfStock = stockQuantities.Where(x => x.Qty < 0);

现在使用Aggregate 构建结果：

var outOfStockRanges =
    outOfStock
        .Skip(1)
        .Aggregate(
            outOfStock
                .Take(1)
                .Select(x => new { From = x.Date, To = x.Date })
                .ToList(),
            (a, x) =>
            {
                if (a.Last().To.AddDays(1.0) == x.Date)
                    a[a.Count - 1] = new { From = a.Last().From, To = x.Date };
                else
                    a.Add(new { From = x.Date, To = x.Date });
                return a;
            });

这是我得到的结果：

Answer 4

我想出了以下几点：

var src_objects = new []
{
    new {date = DateTime.Parse("2014-02-03"), qty = 6},
    new {date = DateTime.Parse("2014-02-04"), qty = -1},
    new {date = DateTime.Parse("2014-02-05"), qty = -2},
    new {date = DateTime.Parse("2014-02-06"), qty = 2},
    new {date = DateTime.Parse("2014-02-07"), qty = -1},
    new {date = DateTime.Parse("2014-02-08"), qty = -2},
    new {date = DateTime.Parse("2014-02-09"), qty = -3},
    new {date = DateTime.Parse("2014-02-10"), qty = 5}
};


int i = 0;


var ranges = src_objects
    .OrderBy(key => key.date)
    .Select(obj =>
    {
        if (obj.qty > 0)
        {
            ++i;
            return new { date = obj.date, group_key = 0 };
        }
        else
            return new { date = obj.date, group_key = i };
    })
    .Where(obj => obj.group_key != 0)
    .GroupBy(obj => obj.group_key)
    .Select(g => new { fromdate = g.First().date, todate = g.Last().date });

ranges
.ToList()
.ForEach(range => Console.WriteLine(string.Format("{0} - {1}", range.fromdate, range.todate.Date)));