我有两个表:

首先是TimeValues(示例)

time | value
12/28/18 | 5.6
01/03/19 | 5.6
01/04/19 | 5.6
01/09/19 | 5.6
01/15/19 | 5.6
02/03/19 | 5.6

其次是 LogicalPeriods

DateFrom | DateTo
12/16/18 | 12/23/18
12/23/18 | 12/30/18
12/30/18 | 01/06/19
01/06/19 | 01/13/19
01/13/19 | 01/20/19
01/20/19 | 01/27/19
01/27/19 | 02/03/19
02/03/19 | 02/10/19

我需要使用 Linq 将 TimeValues 表与 LogicalPeriods 表进行分组(time 必须 > DateFrom 和 <= DateTo)，结果表将有两列 DateTo Và SUM(value)，如果两者之间没有任何时间值期间，只需返回 null。来 self 的例子

DateTo | value
12/23/18 | null
12/30/18 | 5.6
01/06/19 | 11.2
01/13/19 | 5.6
01/20/19 | 5.6
01/27/19 | null
02/03/19 | 5.6
02/10/19 | null

这是我到目前为止的一个例子

var TimeValues = new List
{
    new TimeValue {time = DateTime.Parse("12/28/18"), value = 5.6 },
    new TimeValue {time = DateTime.Parse("01/03/19"), value = 5.6 },
    new TimeValue {time = DateTime.Parse("01/04/19"), value = 5.6 },
    new TimeValue {time = DateTime.Parse("01/09/19"), value = 5.6 },
    new TimeValue {time = DateTime.Parse("01/15/19"), value = 5.6 },
    new TimeValue {time = DateTime.Parse("02/03/19"), value = 5.6 },
};

var LogicalPeriods = new List
{
    new LogicalPeriod { DateFrom = DateTime.Parse("12/28/18"), DateTo = DateTime.Parse("12/23/18") },
    new LogicalPeriod { DateFrom = DateTime.Parse("12/23/18"), DateTo = DateTime.Parse("12/30/18") },
    new LogicalPeriod { DateFrom = DateTime.Parse("12/30/18"), DateTo = DateTime.Parse("01/06/19") },
    new LogicalPeriod { DateFrom = DateTime.Parse("01/06/19"), DateTo = DateTime.Parse("01/13/19") },
    new LogicalPeriod { DateFrom = DateTime.Parse("01/13/19"), DateTo = DateTime.Parse("01/20/19") },
    new LogicalPeriod { DateFrom = DateTime.Parse("01/20/19"), DateTo = DateTime.Parse("01/27/19") },
    new LogicalPeriod { DateFrom = DateTime.Parse("01/27/19"), DateTo = DateTime.Parse("02/03/19") },
    new LogicalPeriod { DateFrom = DateTime.Parse("02/03/19"), DateTo = DateTime.Parse("02/10/19") },
};

var result = LogicalPeriods.GroupJoin(
    TimeValues,
    period => new { period.DateFrom, period.DateTo },
    tv => tv.time,
    (period, tv) => new {period.DateTo, timeValues = tv })// I don't know what should I need do here

tôi đã tìm thấy GroupJoin 仅使用相等比较器，但我需要进行比较。将有助于建议使用方法语法的解决方案。

câu trả lời hay nhất

使用以下逻辑我能够得到上面显示的预期结果

CultureInfo provider = CultureInfo.InvariantCulture;
var timeValues = new List
{
    new TimeValue {time = DateTime.ParseExact("12/28/18","MM/dd/yy",provider), value = 5.6 },
    new TimeValue {time = DateTime.ParseExact("01/03/19","MM/dd/yy",provider), value = 5.6 },
    new TimeValue {time = DateTime.ParseExact("01/04/19","MM/dd/yy",provider), value = 5.6 },
    new TimeValue {time = DateTime.ParseExact("01/09/19","MM/dd/yy",provider), value = 5.6 },
    new TimeValue {time = DateTime.ParseExact("01/15/19","MM/dd/yy",provider), value = 5.6 },
    new TimeValue {time = DateTime.ParseExact("02/03/19","MM/dd/yy",provider), value = 5.6 },
};

var logicalPeriods = new List
{
    new LogicalPeriod { DateFrom = DateTime.ParseExact("12/28/18","MM/dd/yy",provider), DateTo = DateTime.ParseExact("12/23/18","MM/dd/yy",provider) },
    new LogicalPeriod { DateFrom = DateTime.ParseExact("12/23/18","MM/dd/yy",provider), DateTo = DateTime.ParseExact("12/30/18","MM/dd/yy",provider) },
    new LogicalPeriod { DateFrom = DateTime.ParseExact("12/30/18","MM/dd/yy",provider), DateTo = DateTime.ParseExact("01/06/19","MM/dd/yy",provider) },
    new LogicalPeriod { DateFrom = DateTime.ParseExact("01/06/19","MM/dd/yy",provider), DateTo = DateTime.ParseExact("01/13/19","MM/dd/yy",provider) },
    new LogicalPeriod { DateFrom = DateTime.ParseExact("01/13/19","MM/dd/yy",provider), DateTo = DateTime.ParseExact("01/20/19","MM/dd/yy",provider) },
    new LogicalPeriod { DateFrom = DateTime.ParseExact("01/20/19","MM/dd/yy",provider), DateTo = DateTime.ParseExact("01/27/19","MM/dd/yy",provider) },
    new LogicalPeriod { DateFrom = DateTime.ParseExact("01/27/19","MM/dd/yy",provider), DateTo = DateTime.ParseExact("02/03/19","MM/dd/yy",provider) },
    new LogicalPeriod { DateFrom = DateTime.ParseExact("02/03/19","MM/dd/yy",provider), DateTo = DateTime.ParseExact("02/10/19","MM/dd/yy",provider) },
};


var result = logicalPeriods.GroupJoin(timeValues,
    p => p,
    t => logicalPeriods.FirstOrDefault(l => t.time > l.DateFrom && t.time <= l.DateTo),
    (p, times) => new {
        p.DateTo,
        value = times.Count() > 0 ? (double?)times.Sum(t => t.value) : null
    }
);

产生预期的结果

DateTo | value
12/23/18 | null
12/30/18 | 5.6
01/06/19 | 11.2
01/13/19 | 5.6
01/20/19 | 5.6
01/27/19 | null
02/03/19 | 5.6
02/10/19 | null

但是，正如@IvanStoev 在评论中提到的

The truth (hence the answer) is that there is no good standard LINQ solution for this type of problem (there are efficient non LINQ algorithmic solutions though).

这样我就能够使用

var result = logicalPeriods.Select(p => new 
{ 
    p.DateTo, 
    value = timeValues.Where(t => t.time > p.DateFrom && t.time <= p.DateTo).Sum(t => t.value) 
}).ToList();

虽然产生与原始解决方案相似的结果，但在处理大型结果集时两者都不是很有效。

关于c# - GroupJoin by date where date in second list between two dates from first，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/54146496/