如何使用"Linq to Objects"将一组连续的日期放在一组中? [英] How can I use "Linq to Objects" to put a set of contiguous dates in one group?

问题描述

我有一个麻烦的查询要写.我目前正在写一些讨厌的for循环来解决它，但我很好奇Linq是否可以为我做这件事.

I have a troublesome query to write. I'm currently writing some nasty for loops to solve it, but I'm curious to know if Linq can do it for me.

我有:

struct TheStruct
{
 public DateTime date {get; set;} //(time portion will always be 12 am)
 public decimal A {get; set;}
 public decimal B {get; set;}
}

以及包含这些结构的列表.假设它是这样订购的:

and a list that contains these structs. Let's say it's ordered this way:

List<TheStruct> orderedList = unorderedList.OrderBy(x => x.date).ToList();

如果将orderedList结构日期放入集合中，则它们相对于日期将始终是连续的.也就是说，如果列表中的最新日期是2011/01/31，并且列表中最早的日期是2011 /01/01，那么您会发现列表中包含31个项目，一月的每个日期都包含一个项目.

If you put the orderedList struct dates in a set they will always be contiguous with respect to the day.. that is if the latest date in the list was 2011/01/31, and the earliest date in the list was 2011/01/01, then you'd find that the list would contain 31 items, one for each date in January.

好，所以我想对列表项进行分组，例如:

Ok, so what I want to do is group the list items such that:

1. 组中的每个项目必须包含相同的十进制A值和相同的十进制B值
2. 如果日期值按顺序排列，则组中的日期值必须形成一组连续的日期
3. 如果您将每个组中的项目总数相加，则总数将等于原始列表中的项目数(或者您可以说具有特定日期的结构不能属于多个组) li>

任何Linq大师都知道该怎么做?

Any Linq masters know how to do this one?

谢谢！

推荐答案

您可以使用 GroupAdjacent扩展方法将序列中的相邻项目分组(见下文):

You can group adjacent items in a sequence using the GroupAdjacent Extension Method (see below):

var result = unorderedList
    .OrderBy(x => x.date)
    .GroupAdjacent((g, x) => x.A == g.Last().A && 
                             x.B == g.Last().B && 
                             x.date == g.Last().date.AddDays(1))
    .ToList();

示例:

(1,1) 2011-01-01   \
(1,1) 2011-01-02    >  Group 1
(1,1) 2011-01-03 __/
(2,1) 2011-01-04   \
(2,1) 2011-01-05    >  Group 2
(2,1) 2011-01-06 __/
(1,1) 2011-01-07   \
(1,1) 2011-01-08    >  Group 3
(1,1) 2011-01-09 __/
(1,1) 2011-02-01   \
(1,1) 2011-02-02    >  Group 4
(1,1) 2011-02-03 __/

扩展方法:

static IEnumerable<IEnumerable<T>> GroupAdjacent<T>(
    this IEnumerable<T> source, Func<IEnumerable<T>, T, bool> adjacent)
{
    var g = new List<T>();
    foreach (var x in source)
    {
        if (g.Count != 0 && !adjacent(g, x))
        {
            yield return g;
            g = new List<T>();
        }
        g.Add(x);
    }
    yield return g;
}

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