我正在为一个自定义应用程序编写Excel导出器，关于C#中的LINQ分组，我有一个问题。
基本上，这个新的Excel导出器类会给定两个日期。然后该类检索在该日期范围内的所有货运。
作为此导出器的一部分，我需要能够按周将日期分组，并获得该周的值。因此，例如，如果我提供了07/12/2011和22/12/2011（dd/MM/yyyy格式），我需要将它们之间的所有货运分组到周中（每周从星期日开始）。使用上述日期的理想结果如下:
Week 1: (consignments between 04/12/2011 and 10/12/2011)
Week 2: (consignments between 11/12/2011 and 17/12/2011)
Week 3: (consignments between 18/11/2011 and 24/12/2011)
有什么想法吗？
这里的基本问题是如何将一个 DateTime 实例投射到一年中的周值。可以通过调用 Calendar.GetWeekOfYear 来实现。因此定义投影方式如下：
Func<DateTime, int> weekProjector =
d => CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(
d,
CalendarWeekRule.FirstFourDayWeek,
DayOfWeek.Sunday);
通过调整方法调用中的参数，您可以精确配置“周数”是如何确定的。如果您愿意，还可以决定将投影定义为扩展方法；这不会改变代码的本质。无论如何，您现在已经准备好按周分组：
var consignmentsByWeek = from con in consignments
group con by weekProjector(con.Date);
如果您还想将输出限制为两个特定日期之间的货运，请添加一个适当的where语句；分组逻辑不会改变。
new { Year = date.Year, weekProjector(date) } 或 date.Year + "-" + weekProjector(date) 使2011年1月1日与当年的圣诞节到新年前夕的12个月后分组。group by date.AddDays(-(int)date.DayOfWeek)
按日期分组.AddDays(((int)date.DayOfWeek) < 4 ? (-(int)date.DayOfWeek) : (-(int)date.DayOfWeek + 7)) - g2serverJon的回答，你还可以获取一周中第一天的日期，然后按该日期进行分组。public static class DateTimeExtensions
{
public static DateTime StartOfWeek(this DateTime dt, DayOfWeek startOfWeek)
{
int diff = dt.DayOfWeek - startOfWeek;
if (diff < 0)
{
diff += 7;
}
return dt.AddDays(-1 * diff).Date;
}
}
var consignmentsByWeek = from con in consignments
group con by con.Datedate.StartOfWeek(DayOfWeek.Monday);
我注意到原帖中的理想输出中有第1周、第2周等。这些不是一年中的周数，而是基于寄售日期显示的周的“索引”。在其他已提供答案的基础上，以下是我的解决方案：
void DoExample()
{
//Load some sample data
var range = new List<DateTime>();
var curDate = DateTime.ParseExact("07/12/2011", "dd/MM/yyyy", System.Globalization.CultureInfo.InvariantCulture);
var maxDate = DateTime.ParseExact("22/12/2011", "dd/MM/yyyy", System.Globalization.CultureInfo.InvariantCulture);
while(curDate < maxDate)
{
range.Add(curDate);
curDate = curDate.AddDays(1);
}
//Run the method to get the consignments
var c = GetConsignments(range, DayOfWeek.Sunday);
//Output to match OP's "ideal" specs
foreach(var v in c)
{
Console.WriteLine($"Week {v.EntryIndex + 1} (number {v.WeekOfYear} in year): (consignments between {v.RangeStart:dd/MM/yyyy} and {v.RangeEnd:dd/MM/yyyy}). Actual date range is {v.RangeStart:dd/MM/yyyy}-{v.RangeEnd:dd/MM/yyyy} ({(v.FullWeek ? "Full" : "Partial")} week)");
}
//Most other answers place a lot of value on the week of the year, so this would include that.
// Also includes the actual date range contained in the set and whether all dates in that week are present
foreach (var v in c)
{
Console.WriteLine($"Week {v.EntryIndex + 1} (number {v.WeekOfYear} in year): (consignments between {v.RangeStart} and {v.RangeEnd})");
}
}
//Note that this lets us pass in what day of the week is the start.
// Not part of OP's requirements, but provides added flexibility
public List<ConsignmentRange> GetConsignments(IEnumerable<DateTime>consignments, DayOfWeek startOfWeek=DayOfWeek.Sunday)
{
return consignments
.OrderBy(v => v)
.GroupBy(v => v.AddDays(-(int)((7 - (int)startOfWeek) + (int)v.DayOfWeek) % 7))
.Select((v, idx) => new ConsignmentRange
{
//These are part of the OP's requirement
EntryIndex = idx,
RangeStart = v.Key, // part of requirement
RangeEnd = v.Key.AddDays(6), // part of requirement
//These are added as potentially useful
WeekOfYear = CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(
v.Key, CalendarWeekRule.FirstFourDayWeek, startOfWeek),
FirstDate = v.Min(),
LastDate = v.Max(),
FullWeek = (v.Distinct().Count() == 7)
}
)
.ToList();
}
public class ConsignmentRange
{
public int EntryIndex;
public int WeekOfYear;
public bool FullWeek;
public DateTime FirstDate;
public DateTime LastDate;
public DateTime RangeStart;
public DateTime RangeEnd;
}
@foreach (var years in _dateRange.GroupBy(y => y.Year))
{
<p>@years.Key</p>
foreach (var months in years.GroupBy(m => m.Month))
{
<p>@CultureInfo.CurrentCulture.DateTimeFormat.GetMonthName(months.Key)</p>
foreach (var weeks in months.GroupBy(w => w.AddDays(-(int)w.DayOfWeek)))
{
<p>@weeks.Key.ToString("dd-MMM-yy")</p>
}
}
}