c# - C# Linq 或 Lambda 表达式 Group by Week IEnumerable 列表与日期字段

Question

我正在尝试对IEnumerable<Object>按周分组的查询进行查询，例如：

Project(Name, DateStart,ID)

我有IEnumerable<Project>并且我想做一份报告，按周分组。

例如：

Week 1
 Project1  8/4/2013 ID1
 Project2  9/4/2013 ID2
Week 2
 Project1  16/4/2013 ID3
 Project2  18/4/2013 ID5
Week 3
 Project1  24/4/2013 ID7
 Project2  26/4/2013 ID8

如果有人可以帮我一把，我真的很感激！我试图做一个 lambda 表达式但没有成功。

谢谢！

Answer 1

var weekGroups = projects
    .Select(p => new 
    { 
        Project = p, 
        Year = p.DateStart.Year, 
        Week =  CultureInfo.InvariantCulture.Calendar.GetWeekOfYear
                      (p.DateStart, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday)
    })
    .GroupBy(x => new { x.Year, x.Week })
    .Select((g, i) => new 
    { 
        WeekGroup = g, 
        WeekNum = i + 1,
        Year = g.Key.Year,
        CalendarWeek = g.Key.Week
    });

foreach (var projGroup in weekGroups)
{
    Console.WriteLine("Week " + projGroup.WeekNum);
    foreach(var proj in projGroup.WeekGroup)
        Console.WriteLine("{0} {1} {2}", 
            proj.Project.Name, 
            proj.Project.DateStart.ToString("d"), 
            proj.Project.ID);
}

Answer 2

您将需要定义一个函数来确定日期在哪一周：

int GetWeek(DateTime date) { ... }

然后 LINQ 查询分组是：

IEnumerable<IGrouping<int, Project>> groupedProjects = 
         myListOfProjects.GroupBy(p => GetWeek(p.DateStart));

您可以遍历分组的项目列表：

foreach (var weekGroup in groupedProjects)
{
    int week = weekGroup.Key;
    foreach (var project in weekGroup)
    {
        Console.WriteLine("Week " + week + " | Project: " + project.ID);
    }
}

Answer 3

我认为只需一个简单的投影就足够了：

// we'll just use the existing settings on the box.
DateTimeFormatInfo dfi = DateTimeFormatInfo.CurrentInfo;
var cal = dfi.Calendar;

var Projects = GetProjectsFromSomewhere(); // assuming IEnumerable<Project>

int week = 1; // this *could* be changed and projected in the Select instead.
foreach (var wg in from p in Projects
    group p by cal.GetWeekOfYear(
        p.StartDate, dfi.CalendarWeekRule, dfi.FirstDayOfWeek))
{
    Console.WriteLine("Week {0}", week);

    foreach (var p in wg)
    {
        Console.WriteLine("    {0} {1} {2}", p.Name, p.StartDate, p.ID);
    }
    week++;
}

Answer 4

我认为为了简化此任务，您可以将 WeekNumber 属性添加到 Project 类中，并在您可以轻松按 WeekNumber 属性分组后在创建 Project 对象时填充它

Project(Name, DateStart,ID,WeekNumber)

Answer 5

您可以使用此处GetWeekOfMonth发布的扩展：

然后执行以下操作：

        var groups = projects.GroupBy(p => p.Start.GetWeekOfMonth());

        foreach (var group in groups)
        {
            Console.WriteLine("Week {0}", group.Key);
            foreach (var project in group)
            {
                Console.WriteLine("\t{0} | {1:dd/MM/yyyy} | {2}", 
                     project.Name, project.Start, project.Id);
            }
        }

Answer 6

除了Tim Schmelter's回答之外，您还可以获取一周中第一天的日期，然后按该日期分组。

获取一周中第一天的日期。您可以使用以下代码：

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;
    }
}

然后你可以像这样按一周的第一个日期分组：

var weekGroups = projects
    .Select(p => new 
    { 
        Project = p
    })
    .GroupBy(x => x.Project.DateStart.StartOfWeek(DayOfWeek.Monday))
    .Select((g, i) => new 
    { 
        WeekGroup = g, 
        WeekNum = i + 1
    });

foreach (var projGroup in weekGroups)
{
    Console.WriteLine("Week " + projGroup.WeekNum);
    foreach(var proj in projGroup.WeekGroup)
        Console.WriteLine("{0} {1} {2}", 
            proj.Project.Name, 
            proj.Project.DateStart.ToString("d"), 
            proj.Project.ID);
}