从周数计算date
任何人都知道一个简单的方法来获得一周的第一天的date（星期一在这里在欧洲）。 我知道年份和周数？ 我打算用C＃来做这件事。
提前致谢。
即使通过@RobinAndersson修复，我也遇到了@HenkHolterman解决scheme的问题。
阅读ISO 8601标准很好地解决了这个问题。 使用第一个星期四作为目标，而不是星期一。 下面的代码也适用于2009年第53周。
public static DateTime FirstDateOfWeekISO8601(int year, int weekOfYear) { DateTime jan1 = new DateTime(year, 1, 1); int daysOffset = DayOfWeek.Thursday - jan1.DayOfWeek; DateTime firstThursday = jan1.AddDays(daysOffset); var cal = CultureInfo.CurrentCulture.Calendar; int firstWeek = cal.GetWeekOfYear(firstThursday, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday); var weekNum = weekOfYear; if (firstWeek <= 1) { weekNum -= 1; } var result = firstThursday.AddDays(weekNum * 7); return result.AddDays(-3); } 注意
下面的答案使用.NET日历规则。 它不承诺ISO8601一致性。 当你需要的时候，看一些其他的答案。 周编号是一团糟，总是试图找出你需要先遵循什么规则。
下面的代码正确地把2009年第一周的开始在29-12-2008。 CalendarWeekRule可能应该是一个参数。
请注意，weekNum应该是> = 1
static DateTime FirstDateOfWeek(int year, int weekNum, CalendarWeekRule rule) { Debug.Assert(weekNum >= 1); DateTime jan1 = new DateTime(year, 1, 1); int daysOffset = DayOfWeek.Monday - jan1.DayOfWeek; DateTime firstMonday = jan1.AddDays(daysOffset); Debug.Assert(firstMonday.DayOfWeek == DayOfWeek.Monday); var cal = CultureInfo.CurrentCulture.Calendar; int firstWeek = cal.GetWeekOfYear(firstMonday, rule, DayOfWeek.Monday); if (firstWeek <= 1) { weekNum -= 1; } DateTime result = firstMonday.AddDays(weekNum * 7); return result; }
我喜欢Henk Holterman提供的解决scheme。 但要多一点文化独立，你必须得到当前文化的一周的第一天（这不总是星期一）：
using System.Globalization; static DateTime FirstDateOfWeek(int year, int weekOfYear) { DateTime jan1 = new DateTime(year, 1, 1); int daysOffset = (int)CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek - (int)jan1.DayOfWeek; DateTime firstMonday = jan1.AddDays(daysOffset); int firstWeek = CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(jan1, CultureInfo.CurrentCulture.DateTimeFormat.CalendarWeekRule, CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek); if (firstWeek <= 1) { weekOfYear -= 1; } return firstMonday.AddDays(weekOfYear * 7); }
最简单的方法可能是find一年中的第一个星期一，然后添加相关的周数。 这是一些示例代码。 它假定一个星期从1开始，顺便说一下：
using System; class Test { static void Main() { // Show the third Tuesday in 2009. Should be January 20th Console.WriteLine(YearWeekDayToDateTime(2009, DayOfWeek.Tuesday, 3)); } static DateTime YearWeekDayToDateTime(int year, DayOfWeek day, int week) { DateTime startOfYear = new DateTime (year, 1, 1); // The +7 and %7 stuff is to avoid negative numbers etc. int daysToFirstCorrectDay = (((int)day - (int)startOfYear.DayOfWeek) + 7) % 7; return startOfYear.AddDays(7 * (week-1) + daysToFirstCorrectDay); } }
就我个人而言，我会利用文化信息来获得一周中的第一天，然后回到文化的第一天。 我不知道我是否正确地解释它，这里是一个例子：
public DateTime GetFirstDayOfWeek(int year, int weekNumber) { return GetFirstDayOfWeek(year, weekNumber, Application.CurrentCulture); } public DateTime GetFirstDayOfWeek(int year, int weekNumber, System.Globalization.CultureInfo culture) { System.Globalization.Calendar calendar = culture.Calendar; DateTime firstOfYear = new DateTime(year, 1, 1, calendar); DateTime targetDay = calendar.AddWeeks(firstOfYear, weekNumber); DayOfWeek firstDayOfWeek = culture.DateTimeFormat.FirstDayOfWeek; while (targetDay.DayOfWeek != firstDayOfWeek) { targetDay = targetDay.AddDays(-1); } return targetDay; }
根据瑞典使用的 ISO 8601：1988 ，今年的第一周是新年之内至less四天的第一周。
所以，如果你的星期在星期一开始，那么每年的第一个星期四在第一个星期内。 你可以从这个DateAdd或DateDiff。
使用Fluent DateTime http://fluentdatetime.codeplex.com/
var year = 2009; var firstDayOfYear = new DateTime(year, 1, 1); var firstMonday = firstDayOfYear.Next(DayOfWeek.Monday); var weeksDateTime = 12.Weeks().Since(firstMonday);
以下是一种与Google Analytics（分析）的星期编号兼容的方法，也是我们在英特尔内部使用的相同编号scheme，而且我确定这种方法也可用于其他许多情况。
// Google Analytics does not follow ISO standards for date. // It numbers week 1 starting on Jan. 1, regardless what day of week it starts on. // It treats Sunday as the first day of the week. // The first and last weeks of a year are usually not complete weeks. public static DateTime GetStartDateTimeFromWeekNumberInYear(int year, uint weekOfYear) { if (weekOfYear == 0 || weekOfYear > 54) throw new ArgumentException("Week number must be between 1 and 54! (Yes, 54... Year 2000 had Jan. 1 on a Saturday plus 53 Sundays.)"); // January 1 -- first week. DateTime firstDayInWeek = new DateTime(year, 1, 1); if (weekOfYear == 1) return firstDayInWeek; // Get second week, starting on the following Sunday. do { firstDayInWeek = firstDayInWeek.AddDays(1); } while (firstDayInWeek.DayOfWeek != DayOfWeek.Sunday); if (weekOfYear == 2) return firstDayInWeek; // Now get the Sunday of whichever week we're looking for. return firstDayInWeek.AddDays((weekOfYear - 2)*7); }
假设周数从1开始
DateTime dt = new DateTime(YearNumber, 1, 1).AddDays((WeekNumber - 1) * 7 - (WeekNumber == 1 ? 0 : 1)); return dt.AddDays(-(int)dt.DayOfWeek);
这应该给你在任何一个星期的第一天。 我没有做过很多的testing，但看起来像是有效的。 它比我在网上find的其他大多数的解决scheme都小，所以想要分享。
.NET的免费时间库包括ISO 8601符合类周 ：
// ---------------------------------------------------------------------- public static DateTime GetFirstDayOfWeek( int year, int weekOfYear ) { return new Week( year, weekOfYear ).FirstDayStart; } // GetFirstDayOfWeek
这一个为我工作，它也有期待一个文化信息作为参数来testing不同文化的公式的优势。 如果为空，则获得当前的文化信息…有效值如“it”，“en-us”，“fr”，… ando等。 诀窍是减去一年中第一天的周数，也就是1表示第一天在第一周内。 希望这可以帮助。
Public Shared Function FirstDayOfWeek(ByVal year As Integer, ByVal weekNumber As Integer, ByVal culture As String) As Date Dim cInfo As System.Globalization.CultureInfo If culture = "" Then cInfo = System.Globalization.CultureInfo.CurrentCulture Else cInfo = System.Globalization.CultureInfo.CreateSpecificCulture(culture) End If Dim calendar As System.Globalization.Calendar = cInfo.Calendar Dim firstOfYear As DateTime = New DateTime(year, 1, 1, calendar) Dim firstDayWeek As Integer = calendar.GetWeekOfYear(firstOfYear, cInfo.DateTimeFormat.CalendarWeekRule, cInfo.DateTimeFormat.FirstDayOfWeek) weekNumber -= firstDayWeek Dim targetDay As DateTime = calendar.AddWeeks(firstOfYear, weekNumber) Dim fDayOfWeek As DayOfWeek = cInfo.DateTimeFormat.FirstDayOfWeek While (targetDay.DayOfWeek <> fDayOfWeek) targetDay = targetDay.AddDays(-1) End While Return targetDay End Function
轻轻改变了Mikael Svenson的代码。 我find了第一个星期一的星期，并适当地改变了星期的数字。
DateTime GetFirstWeekDay(int year, int weekNum) { Calendar calendar = CultureInfo.CurrentCulture.Calendar; DateTime jan1 = new DateTime(year, 1, 1); int daysOffset = DayOfWeek.Monday - jan1.DayOfWeek; DateTime firstMonday = jan1.AddDays(daysOffset); int firstMondayWeekNum = calendar.GetWeekOfYear(firstMonday, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday); DateTime firstWeekDay = firstMonday.AddDays((weekNum-firstMondayWeekNum) * 7); return firstWeekDay; }
我尝试了一些上面的代码，一些有一些小错误，当你尝试不同的年份，在不同的开始几天你会看到他们，我拿了乔恩Skeet的代码，修复它，它的工作，非常简单的代码。
Public Function YearWeekDayToDateTime(ByVal year As Integer, ByVal weekDay As Integer, ByVal week As Integer) As DateTime ' weekDay, day you want Dim startOfYear As New DateTime(year, 1, 1) Dim startOfYearFixDay As Integer If startOfYear.DayOfWeek <> DayOfWeek.Sunday Then startOfYearFixDay = startOfYear.DayOfWeek Else startOfYearFixDay = 7 End If Return startOfYear.AddDays((7 * (week)) - startOfYearFixDay + weekDay) End Function
第1周定义为星期一开始的星期，包含一年中的第一个星期四。
要在两个方向转换，请参阅此处： 关于ISO周date的维基百科文章
我用一个覆盖改进了一下托马斯的解决scheme：
public static DateTime FirstDateOfWeek(int year, int weekOfYear) { return Timer.FirstDateOfWeekOfMonth(year, 1, weekOfYear); } public static DateTime FirstDateOfWeekOfMonth(int year, int month, int weekOfYear) { DateTime dtFirstDayOfMonth = new DateTime(year, month, 1); //I also commented out this part: /* if (firstWeek <= 1) { weekOfYear -= 1; } */
否则，date前一周。
谢谢托马斯，很有帮助。
我使用了其中的一个解决scheme，但它给了我错误的结果，仅仅是因为它将星期天定为一周中的第一天。
我变了：
var firstDay = new DateTime(DateTime.Now.Year, 1, 1).AddDays((weekNumber - 1) * 7); var lastDay = firstDay.AddDays(6);
至：
var lastDay = new DateTime(DateTime.Now.Year, 1, 1).AddDays((weekNumber) * 7); var firstDay = lastDay.AddDays(-6);
现在它正在成为一种魅力。
build议的解决scheme不完整 – 它只适用于CalendarWeekRule.FirstFullWeek。 其他types的周规则不起作用。 使用这个testing用例可以看出这一点：
foreach (CalendarWeekRule rule in Enum.GetValues(typeof(CalendarWeekRule))) { for (int year = 1900; year < 2000; year++) { DateTime date = FirstDateOfWeek(year, 1, rule); Assert(CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(date, rule, DayOfWeek.Monday) == 1); Assert(CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(date.AddDays(-1), rule, DayOfWeek.Monday) != 1); } }
我已经提出了一个更简单的参数化的build议解决scheme的精炼版本，并将参数化为firstDayOfWeek：
public static DateTime GetFirstDayOfWeek(int year, int week, DayOfWeek firstDayOfWeek) { return GetWeek1Day1(year, firstDayOfWeek).AddDays(7 * (week - 1)); } public static DateTime GetWeek1Day1(int year, DayOfWeek firstDayOfWeek) { DateTime date = new DateTime(year, 1, 1); // Move towards firstDayOfWeek date = date.AddDays(firstDayOfWeek - date.DayOfWeek); // Either 1 or 52 or 53 int weekOfYear = CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(date, CalendarWeekRule.FirstFullWeek, firstDayOfWeek); // Move forwards 1 week if week is 52 or 53 date = date.AddDays(7 * System.Math.Sign(weekOfYear - 1)); return date; }
这是我的解决scheme，当我们要计算一个给定的年份，周数和星期几的date。
int Year = 2014; int Week = 48; int DayOfWeek = 4; DateTime FecIni = new DateTime(Year, 1, 1); FecIni = FecIni.AddDays(7 * (Week - 1)); if ((int)FecIni.DayOfWeek > DayOfWeek) { while ((int)FecIni.DayOfWeek != DayOfWeek) FecIni = FecIni.AddDays(-1); } else { while ((int)FecIni.DayOfWeek != DayOfWeek) FecIni = FecIni.AddDays(1); }
我简化了Mikael Svensson提供的欧洲许多国家正确的代码。
public static DateTime FirstDateOfWeekIso8601(int year, int week) { var firstThursdayOfYear = new DateTime(year, 1, 1); while (firstThursdayOfYear.DayOfWeek != DayOfWeek.Thursday) { firstThursdayOfYear = firstThursdayOfYear.AddDays(1); } var startDateOfWeekOne = firstThursdayOfYear.AddDays(-(DayOfWeek.Thursday - DayOfWeek.Monday)); return startDateOfWeekOne.AddDays(7 * (week - 1)); }
我已经编写和testing了下面的代码，对我来说工作得很好。 请让我知道如果有人遇到麻烦，我也发布了一个问题，以获得最佳答案。 有人可能会觉得它有用。
public static DateTime GetFirstDateOfWeekByWeekNumber(int year, int weekNumber) { var date = new DateTime(year, 01, 01); var firstDayOfYear = date.DayOfWeek; var result = date.AddDays(weekNumber * 7); if (firstDayOfYear == DayOfWeek.Monday) return result.Date; if (firstDayOfYear == DayOfWeek.Tuesday) return result.AddDays(-1).Date; if (firstDayOfYear == DayOfWeek.Wednesday) return result.AddDays(-2).Date; if (firstDayOfYear == DayOfWeek.Thursday) return result.AddDays(-3).Date; if (firstDayOfYear == DayOfWeek.Friday) return result.AddDays(-4).Date; if (firstDayOfYear == DayOfWeek.Saturday) return result.AddDays(-5).Date; return result.AddDays(-6).Date; }
目前，没有正确处理ISO 8601周编号的C＃类。 即使你可以实例化一个文化，寻找最接近的东西，并纠正这一点，我认为最好自己做一个完整的计算：
/// <summary> /// Converts a date to a week number. /// ISO 8601 week 1 is the week that contains the first Thursday that year. /// </summary> public static int ToIso8601Weeknumber(this DateTime date) { var thursday = date.AddDays(3 - date.DayOfWeek.DayOffset()); return (thursday.DayOfYear - 1) / 7 + 1; } /// <summary> /// Converts a week number to a date. /// Note: Week 1 of a year may start in the previous year. /// ISO 8601 week 1 is the week that contains the first Thursday that year, so /// if December 28 is a Monday, December 31 is a Thursday, /// and week 1 starts January 4. /// If December 28 is a later day in the week, week 1 starts earlier. /// If December 28 is a Sunday, it is in the same week as Thursday January 1. /// </summary> public static DateTime FromIso8601Weeknumber(int weekNumber, int? year = null, DayOfWeek day = DayOfWeek.Monday) { var dec28 = new DateTime((year ?? DateTime.Today.Year) - 1, 12, 28); var monday = dec28.AddDays(7 * weekNumber - dec28.DayOfWeek.DayOffset()); return monday.AddDays(day.DayOffset()); } /// <summary> /// Iso8601 weeks start on Monday. This returns 0 for Monday. /// </summary> private static int DayOffset(this DayOfWeek weekDay) { return ((int)weekDay + 6) % 7; }
