Is there a possibility to get the full date out of the year and the dayOfYear value?
For example: today is Thursday, 19th of february 2015.
The dayOfYear-Value of today is 50.
If I have the value 75 and the year 2010, how am I able to get the matching date?
It could be displayed in a textBox, dateTimePicker, whatever.
But you only have the information year & dayOfYear.
Thanks
You can use the following code:
DateTime day = New DateTime(2010, 1, 1).AddDays(75 - 1);
First get the first day of the year, then add necessary day count minus one (you are already on the first date of the year) days to the first day and you are there.
Related
In MS Excel with US English culture, while checking the Day of the week for the Date "1/1/1900", it returns SUNDAY, whereas in DayofWeek property of DateTime, it returns MONDAY. Also, checked with the Calender, it shows DayOFWeek for the Date "1/1/1900" is Monday. Hence, can any one please explain the behavior of DayOfWeek in Excel?
January 1, 1990 was a Monday (https://en.wikipedia.org/wiki/January_1900#January_1,1900(Monday))
The "WEEKDAY" Excel function returns a number from 1 (Sunday) to 7 (Saturday) representing the day of the week of a date.
System.DayOfWeek is an enumeration going from 0 (Sunday) to 6 (Saturday) (https://learn.microsoft.com/en-us/dotnet/api/system.datetime.dayofweek?view=netframework-4.8)
You pointed out a well known problem. As explained here, https://support.microsoft.com/en-us/help/214326/excel-incorrectly-assumes-that-the-year-1900-is-a-leap-year
"The WEEKDAY function returns incorrect values for dates before March 1, 1900. Because most users do not use dates before March 1, 1900, this problem is rare."
See also this answer: https://superuser.com/a/481499
This question already has answers here:
Get the correct week number of a given date
(20 answers)
Closed 4 years ago.
I am trying to get the week number from a date time and in my case, the first day of the week is Monday and I want to follow the FirstFourDays convention.
To check the results, I am checking this webpage:
https://espanol.epochconverter.com/semanas/2020
To get the week number, I using the method:
System.Globalization.CultureInfo.InvariantCulture.Calendar.GetWeekOfYear();
So I am trying to get the week number of the date 2019-12-29, so I use this code:
System.Globalization.CultureInfo.InvariantCulture.Calendar.GetWeekOfYear(new DateTime(2019, 12, 29), System.Globalization.CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
The result is week 52. It is correct.
Now I am trying to get the week number of the 2019-12-30, the week number that I get is 53, it is wrong, because 2019 has only 52 weeks. In fact, 2019-12-30 belongs to the same week than 2020-01-01, that it is week 1, that is correct, so I don't understand why I can get two different results for the same date.
How I could get the correct result always? Or how would it be the correct way to get the week number of any date?
There's a blog article explaining this behavior and proposing a solution.
The issue:
Several people have noticed that Calendar.GetWeekOfYear() is almost like the ISO 8601 week when passed CalendarWeekRule.FirstFourDayWeek and DayOfWeek.Monday, however it is a little bit different. Specifically ISO 8601 always has 7 day weeks. If the first partial week of a year doesn't contain Thursday, then it is counted as the last week of the previous year. Likewise, if the last week of the previous year doesn't contain Thursday then its treated like the first week of the next year. GetWeekOfYear() has the first behavior, but not the second.
The proposed solution would be this:
A simple workaround to consistently get the ISO 8601 week is to realize that consecutive days Monday through Sunday in ISO 8601 weeks all have the same week #. So Monday has the same week # as Thursday. Since Thursday is the critical day for determining when the week starts each year my solution is to add 3 days if the day is Monday, Tuesday or Wednesday. The adjusted days are still in the same week, and use values that GetWeekOfYear and ISO 8601 agree on.
// This presumes that weeks start with Monday.
// Week 1 is the 1st week of the year with a Thursday in it.
public static int GetIso8601WeekOfYear(DateTime time)
{
// Seriously cheat. If its Monday, Tuesday or Wednesday, then it'll
// be the same week# as whatever Thursday, Friday or Saturday are,
// and we always get those right
DayOfWeek day = cal.GetDayOfWeek(time);
if (day >= DayOfWeek.Monday && day <= DayOfWeek.Wednesday)
{
time = time.AddDays(3);
}
// Return the week of our adjusted day
return cal.GetWeekOfYear(time, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
}
All credits for this go to Shawn Steele.
I want to decrement the day in DateTimePicker when button is clicked and keep the customized time at 10:00:00.
When I use the following code and when going back from month to another (previous month on the same year) it works fine.
but the problem comes when I try to go back from 2016 to 2015. For example when I try to go back from 1-1-2016 to 31-12-2015 it gives error: "Year, Month, and Day parameters describe an un-representable DateTime"
dateTimePicker1.Value = new DateTime(dateTimePicker1.Value.Year, dateTimePicker1.Value.Month, dateTimePicker1.Value.Day - 1, 10, 00, 0);
Anyone knows how can I decrease the day and keep customized time when going back from year to another (previous year)? please help. Thank you
dateTimePicker1.Value is a DateTime and DateTime has methods to modify dates and times correctly
dateTimePicker1.Value = dateTimePicker1.Value.Date.AddDays(-1).AddHours(10);
It takes current date [midnight], calculates previous date [still midnight] and adds 10 hours [morning]
I have tried searching for a solution which gives the correct week number for the date value.
link1, link2,link3
Followed the methods in the above links, but for the date 30/12/2014, I get the week number as 53. but it falls as 1st week of 2015 year.
I tried the below methods to get the week number of the year for the specific date.
private int GetWeekNumberOfTheYear() {
var currentCulture = CultureInfo.CurrentCulture;
// option 1
var weekNo = currentCulture.Calendar.GetWeekOfYear(DateTime.Now,currentCulture.DateTimeFormat.CalendarWeekRule, currentCulture.DateTimeFormat.FirstDayOfWeek);
// option 2
var weekNo = CultureInfo.InvariantCulture.Calendar.GetWeekOfYear(DateTime.Now, CalendarWeekRule.FirstDay, DayOfWeek.Monday);
return weekNo; }
Is the method above is correct to return 53 as week number or it should be 1 ?
Is there any mistake in the above code. Suggestions please.
EDIT :
Found many searches specified, Dec 29th 2014 to 4th Jan 2015 as 1st week of year 2015.
So my confusion is the present week must be taken as 53rd Week or 1st Week.
http://week-number.net/calendar-with-week-numbers-2014.html
http://www.epochconverter.com/date-and-time/weeknumbers-by-year.php
If you're looking for the ISO-8601 week-of-week-year, you could use my Noda Time project:
var date = new LocalDate(2014, 12, 30);
var week = date.WeekOfWeekYear; // 1
var weekYear = date.WeekYear; // 2015
You can get a LocalDate from a DateTime via a LocalDateTime, but ideally you'd use the Noda Time times as widely as possible through your project. (That's the way I'd hope you'd get the maximum benefit, anyway.)
I just discovered a DateTime math bug in my code today, August 1st, the start of a new month.
I am setting a DateTime class member to the DateTime value of 7 days ago. So the value it should have on August 1st, would be July 25th
I clearly see the problem when trying to subtract 7 from 1 (DateTime.Now.Day-7).
So how do I create a DateTime object that always works regardless of what day of the month it is?
Error:
Year, Month, and Day parameters describe an un-representable DateTime.
Here is the code:
DateFrom = (new DateTime(DateTime.Now.Year, DateTime.Now.Month, DateTime.Now.Day-7));
What is the correct way to set this member to be 7 days ago from current DateTime?
Just subtract seven days from DateTime.Now:
DateFrom = DateTime.Now.Date.AddDays(-7);
DateFrom date = DateTime.Now.AddDays(-7);
You can use the AddDays method of datetime object that takes integer. As it takes negative values as well so you can easily move back in time.
DateFrom = DateTime.Now.AddDays(-7);