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.net core how to get week datetime list by datetime range

I hope get week datetime list by datetime range,I tried the following code get number of weeks per month.
var start = new DateTime(2021, 6, 09);
var end = new DateTime(2021, 7, 01);
end = new DateTime(end.Year, end.Month, DateTime.DaysInMonth(end.Year, end.Month));
var diff = Enumerable.Range(0, Int32.MaxValue)
.Select(e => start.AddMonths(e))
.TakeWhile(e => e <= end)
.Select(e => Convert.ToDateTime(e.ToString("yyyy-MM")));
foreach (var item in diff)
{
DateTime dateTime = item;
Calendar calendar = CultureInfo.CurrentCulture.Calendar;
IEnumerable<int> daysInMonth = Enumerable.Range(1, calendar.GetDaysInMonth(dateTime.Year, dateTime.Month));
List<Tuple<DateTime, DateTime>> weeks = daysInMonth.Select(day => new DateTime(dateTime.Year, dateTime.Month, day))
.GroupBy(d => calendar.GetWeekOfYear(d, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday))
.Select(g => new Tuple<DateTime, DateTime>(g.First(), g.Last()))
.ToList();
}
Executing the above code I got the following result,get all the weeks of each month。
2021-06-01 2021-06-06
......
2021-07-26 2021-07-31
I want to count the week from my start date 2021-06-09 to the end date 2021-07-01, like this.
2021-06-09 2021-06-13
2021-06-14 2021-06-20
2021-06-21 2021-06-27
2021-06-28 2021-07-01
how to changed my code

This will produce the desired output:
var start = new DateTime(2021, 6, 09);
var end = new DateTime(2021, 7, 01);
// If you want to get the first week complete, add this line:
//DateTime currDate = start.AddDays(1-(int)start.DayOfWeek);
// Otherwise, use this one
DateTime currDate = start;
while(currDate <= end){
var dayOfWeek = (int)currDate.DayOfWeek;
var endOfWeek = currDate.AddDays(7 - dayOfWeek);
//If you want the complete last week, omit this if
if(endOfWeek > end)
{
endOfWeek = end;
}
Console.WriteLine($"{currDate:yyyy-MM-dd} {endOfWeek:yyyy-MM-dd}");
currDate = endOfWeek.AddDays(1);
}
output:
2021-06-09 2021-06-13
2021-06-14 2021-06-20
2021-06-21 2021-06-27
2021-06-28 2021-07-01

Lambda between two dates explicit

I am in need of some wizards.
I have a table
Start End PersonID
-----------------------------------------------------
10/07/2017 00:00:00 18/07/2017 00:00:00 1
27/07/2017 00:00:00 27/07/2017 00:00:00 1
28/07/2017 00:00:00 28/07/2017 00:00:00 1
29/07/2017 00:00:00 29/07/2017 00:00:00 1
30/07/2017 00:00:00 30/07/2017 00:00:00 1
If I search for
Date Start = 11/07/2017
Date End = 12/07/2017
Using this query:
DateTime start = new DateTime(2017,07,11,0,0,0,0,0);
DateTime end = start.AddDays(1);
DateTime[] days = new DateTime[end.Subtract(start).Days];
for (int i = 0; i < end.Subtract(start).Days; i++)
{
var d = start.AddDays(i);
days[i] = d;
}
IQueryable block = tmOpen1.Calendar.Where(x => days.All(y => y >= x.start && y <= x.end)).Select(x => new { ID = x.PersonID });`
I get a positive result for ROW 1 (10/07/2017 - 18/07/2017)
However If I apply it against the remaining rows e.g. Filter
Date Start = 28/07/2017
Date End = 29/07/2017
Then obviously this will fail. How Can I get this side of the search to work.
E.g. Either
Take the first row and make it split out into individual rows
Make the Individual rows return true if a Person has several true conditions.
I hope one of the geniuses here can help.

Seems like all you really need is something like this:
DateTime start = new DateTime(2017,07,11,0,0,0,0,0);
DateTime end = start.AddDays(1);
var results = tmOpen1.Calendar
.Where(c => start <= c.end && end >= c.start)
.Select(x => new { ID = x.PersonID });

If your interval starts or ends somewhere between a start and end date from the table, than it means it is overlapping and you should included in your result.
tmOpen1.Calendar.Where(x => (startDate >= x.start && startDate <= x.end) || (endDate >= x.start && endDate <= x.end)).Select(x => new { ID = x.PersonID });
So an interval 10.07 - 27.07 should give you the first 2 rows, right?
Or is the interval supposed to be fully enclosed between 2 dates in the table?

From understanding of your question you want to know when the Date Start or Date End is within a range of dates.
You can check Date Start is within the date range or the Date End is within the date range
Example:
List<DateRange> dates = new List<DateRange>();
dates.Add(new DateRange()
{
StartDate = new DateTime(2017, 07, 10),
EndDate = new DateTime(2017, 07, 18)
});
dates.Add(new DateRange()
{
StartDate = new DateTime(2017, 07, 28),
EndDate = new DateTime(2017, 07, 28)
});
DateRange search1 = new DateRange()
{
StartDate = new DateTime(2017, 07, 11),
EndDate = new DateTime(2017, 07, 12)
};
DateRange search2 = new DateRange()
{
StartDate = new DateTime(2017, 07, 28),
EndDate = new DateTime(2017, 07, 29)
};
var result1 = dates.Where(x => search1.StartDate >= x.StartDate && search1.StartDate <= x.EndDate ||
search1.EndDate <= x.StartDate && search1.EndDate >= x.EndDate);
var result2 = dates.Where(x => search2.StartDate >= x.StartDate && search2.StartDate <= x.EndDate ||
search2.EndDate <= x.StartDate && search2.EndDate >= x.EndDate);

Simplier with the not valid time frame:
DateTime start = new DateTime(2017, 07, 11, 0, 0, 0, 0, 0);
DateTime end = start.AddDays(1);
var results = tmOpen1.Calendar.
.Where( c => ! ( c.Start > end || c.End < start) )
.Select(x => new { ID = x.PersonID } );
For DateTime start = new DateTime(2017, 07, 11, 0, 0, 0, 0, 0);
The result are:
TEST 1: 11/07/2017 00:00:00
Start:10/07/2017 00:00:00 End:18/07/2017 00:00:00 ID:1
For DateTime start = new DateTime(2017, 07, 28, 0, 0, 0, 0, 0);
The result are:
TEST 2: 28/07/2017 00:00:00
Start:28/07/2017 00:00:00 End:28/07/2017 00:00:00 ID:1
Start:29/07/2017 00:00:00 End:29/07/2017 00:00:00 ID:1

modelclassList= modelclassList.Where(x => x.gf_expdate>DateTime.Now).ToList();
to check expiry date and save back list of model class

How to find exact date range from list of date ranges by entering single date

I want to find the date range which falls in input date, following is structure
public class Duration
{
public DateTime StartDate { get; set; }
public DateTime EndDate { get; set; }
}
var durations = new List<Duration>();
var duration1 = new Duration()
{
StartDate = new DateTime(2017, 08, 1),
EndDate = new DateTime(2017, 08, 10)
};
durations.Add(duration1);
var duration2 = new Duration()
{
StartDate = new DateTime(2017, 08, 5),
EndDate = new DateTime(2017, 08, 10)
};
durations.Add(duration2);
var duration3 = new Duration()
{
StartDate = new DateTime(2017, 08, 5),
EndDate = new DateTime(2017, 08, 6)
};
durations.Add(duration3);
Now I want to find duration which is closest to the entered date for list of <Durations> with LINQ or for-loop
My expected result for currentDate=new DateTime(2017, 08, 7); is duration2

You first need to check if the currentDate is within the start and end dates of each range. For the ones that meet that condition, you calculate the "closeness" adding both distances. When you find one lapse(gap) smaller tan the previous, you save its index... and voilá
int lapse = Integer.MaxValue;
int counter = 0;
int index = 0;
foreach (d in durations) {
if (((d.StartDate <= currentDate) && (d.EndDate >= currentDate))) {
int newlapse = ((currentDate - d.StartDate).TotalDays + (d.EndDate - currentDate).TotalDays);
if ((newlapse < lapse)) {
lapse = newlapse;
index = counter;
}
}
counter +=1;
}
return durations(index);

If you need the middle of interval to be closest:
durations.OrderBy((d) => Math.Abs(d.EndDate.Ticks + d.StartDate.Ticks) / 2 - currentDate.Ticks).FirstOrDefault();
If you need the start of interval to be closest:
durations.OrderBy((d) => Math.Abs(d.EndDate.Ticks - currentDate.Ticks)).FirstOrDefault();

As D le mentioned above
First check if currentDate is within the start and end dates
Second select the duration with the minimal difference between start end end date
I used a nuget package called morelinq which gives nice extensions methods like MinBy:
var result = (from d in durations
where (d.StartDate <= currentDate && d.EndDate >= currentDate)
select d).MinBy(d => d.EndDate - d.StartDate);

Linq to Entity Birthday Comparison

I have the requirement to create a query using Linq to Entities where the birthday must fall within 2 days ago and the next 30 days.
The following returns nothing:
DateTime twoDaysAgo = DateTime.Now.AddDays(-2);
int twoDaysAgoDay = twoDaysAgo.Day;
int twoDaysAgoMonth = twoDaysAgo.Month;
DateTime MonthAway = DateTime.Now.AddDays(30);
int monthAwayDay = MonthAway.Day;
int monthAwayMonth = MonthAway.Month;
var bdays = from p in db.Staffs where EntityFunctions.TruncateTime(p.BirthDate) > EntityFunctions.TruncateTime(twoDaysAgo) &&
EntityFunctions.TruncateTime(p.BirthDate) < EntityFunctions.TruncateTime(MonthAway)
orderby p.BirthDate select p;
return bdays;
The problem I'm having is that I need something where if the birthday falls from 11/3 to 12/5, it should return it. The reason it fails because the birthdays include the Year. However, when I use something like:
p.BirthDate.Value.Month
I receive the error that this isn't support with Linq to Entities. Any assistance would be appreciated.

Year-wrapping independent solution:
void Main()
{
var birthdays = new List<DateTime>();
birthdays.Add(new DateTime(2013, 11, 08));
birthdays.Add(new DateTime(2012, 05, 05));
birthdays.Add(new DateTime(2014, 05, 05));
birthdays.Add(new DateTime(2005, 11, 08));
birthdays.Add(new DateTime(2004, 12, 31));
foreach(var date in birthdays.Where(x => x.IsWithinRange(twoDaysAgo, MonthAway))){
Console.WriteLine(date);
}
}
public static class Extensions {
public static bool IsWithinRange(this DateTime #this, DateTime lower, DateTime upper){
if(lower.DayOfYear > upper.DayOfYear){
return (#this.DayOfYear > lower.DayOfYear || #this.DayOfYear < upper.DayOfYear);
}
return (#this.DayOfYear > lower.DayOfYear && #this.DayOfYear < upper.DayOfYear);
}
}
Output with
DateTime twoDaysAgo = DateTime.Now.AddDays(-2);
DateTime MonthAway = DateTime.Now.AddDays(30);
8/11/2013 0:00:00
8/11/2005 0:00:00
Output with
DateTime twoDaysAgo = new DateTime(2012, 12, 25);
DateTime MonthAway = new DateTime(2013, 01, 05);
31/12/2004 0:00:00

If you want to ignore the value of the year, what about using DayOfYear function ?
var bdays = from p in db.Staffs
where EntityFunctions.DayOfYear(p.BirthDate) > EntityFunctions.DayOfYear(twoDaysAgo) &&
EntityFunctions.DayOfYear(p.BirthDate) < EntityFunctions.DayOfYear(MonthAway)
orderby p.BirthDate select p;

You can change all the years to now since year is irrelevant and then you can check it this way
DateTime twoDaysAgo = DateTime.Today.AddDays(-2);
DateTime monthAway = DateTime.Today.AddMonths(1);
List<DateTime> checkDates = new List<DateTime>
{ new DateTime(2011, 11, 3), new DateTime(2011, 12, 5), new DateTime(2011, 12, 6), new DateTime(2011, 11, 2) };
checkDates = checkDates.Select(x => new DateTime(DateTime.Today.Year, x.Month, x.Day)).ToList();
var bdays = from p in checkDates
where (p >= twoDaysAgo && p <= monthAway) ||
(p>= twoDaysAgo.AddYears(-1) && p <= monthAway.AddYears(-1))
orderby p
select p;
This results in
11/3/2013 12:00:00 AM
12/5/2013 12:00:00 AM
This also works with the following list of dates when today is new DateTime(2013, 12, 31)
List<DateTime> checkDates = new List<DateTime>
{ new DateTime(2011, 12, 29), new DateTime(2011, 12, 28), new DateTime(2011, 1, 30), new DateTime(2011, 2, 2) };
Giving the results
1/30/2013 12:00:00 AM
12/29/2013 12:00:00 AM

How about if you add the the nr. of years from the birthdate to today?
Something like:
(untested)
var now = DateTime.Now;
var twoDaysAgo = now.AddDays(-2);
var monthAway = now.Now.AddDays(30)
var bdays =
from p in db.Staffs
let bDay = EntityFunctions.AddYears(p.BirthDate,
EntityFunctions.DiffYears(now, p.BirthDate))
where
bDay > twoDaysAgo &&
bDay < monthAway
orderby p.BirthDate
select p;

Select Only Fourth Sunday of each month

I am stuck for sometime now, now need your help.
I want to display in a dropdown only fourth Sunday of each month, say from 1-Sep-2010 to 31-Aug-2011
I only want fourth Sunday in dropdown list, how to do it using asp.net C#
Regards

Here is an approach that uses a little LINQ and the knowledge that the fourth Sunday will occur between the 22nd and 28th of a month, inclusive.
DateTime startDate = new DateTime(2010, 9, 1);
DateTime endDate = startDate.AddYears(1).AddDays(-1);
List<DateTime> fourthSundays = new List<DateTime>();
DateTime currentDate = startDate;
while (currentDate < endDate)
{
// we know the fourth sunday will be the 22-28
DateTime fourthSunday = Enumerable.Range(22, 7).Select(day => new DateTime(currentDate.Year, currentDate.Month, day)).Single(date => date.DayOfWeek == DayOfWeek.Sunday);
fourthSundays.Add(fourthSunday);
currentDate = currentDate.AddMonths(1);
}
You can then bind that List<DateTime> to the dropdown or skip the list itself in favor of adding the items as you generate them to the dropdown, like below.
yourDropdown.Items.Add(new ListItem(fourthSunday.ToString()));
For giggles, you can do the whole thing in a LINQ statement and skip (most of) the variables.
DateTime startDate = new DateTime(2010, 9, 1);
IEnumerable<DateTime> fourthSundays =
Enumerable.Range(0, 12)
.Select(item => startDate.AddMonths(item))
.Select(currentMonth =>
Enumerable.Range(22, 7)
.Select(day => new DateTime(currentMonth.Year, currentMonth.Month, day))
.Single(date => date.DayOfWeek == DayOfWeek.Sunday)
);

Got bored so here you go. Two helper methods one retrieves the Week if it exist, and the other iterates through the months
class Program
{
static void Main(string[] args)
{
DateTime startDate = new DateTime(2010, 09, 1);
foreach(DateTime dt in EachMonth( new DateTime(2010, 09, 1), new DateTime(2011, 09, 1))){
DateTime? result = GetDayByWeekOffset(DayOfWeek.Sunday, dt, 4);
Console.WriteLine("Sunday:" + (result.HasValue?result.Value.ToString("MM-dd-yyyy"):"null"));
}
Console.ReadKey();
}
public static DateTime? GetDayByWeekOffset(DayOfWeek day, DateTime month, int weekOffSet)
{
//First day of month
DateTime firstDayOfMonth = month.AddDays((-1 * month.Day) + 1);
//
int daysOffSet;
daysOffSet= ((int)day + 7 - (int)firstDayOfMonth.DayOfWeek) % 7;
DateTime firstDay = month.AddDays(daysOffSet);
// Add the number of weeks specified
DateTime resultDate = firstDay.AddDays((weekOffSet - 1) * 7);
if (resultDate.Month != firstDayOfMonth.Month){
return null;
}else{
return resultDate;
}
}
public static IEnumerable<DateTime> EachMonth(DateTime from, DateTime thru)
{
for (var month = from.Date; month.Date <= thru.Date; month = month.AddMonths(1))
yield return month;
}
}

Anthony's answer above is nice, I like it a lot. As an alternate, here is a method which is parameterized for the day of the week and the week number (i.e. if you need other combinations, like 4th Sunday, 3rd Friday, etc.) with some comments.
Call it like this for your case:
List<DateTime> sundays = DateInstances(new DateTime(2010, 9, 1), new DateTime(2011, 8, 31), DayOfWeek.Sunday, 4);
And the method itself:
public List<DateTime> DateInstances(DateTime start, DateTime end, DayOfWeek day, int weeks)
{
if (start > end)
throw new ArgumentOutOfRangeException("end", "The start date must occur before the end date");
List<DateTime> results = new List<DateTime>();
DateTime temp = start;
while (temp < end)
{
DateTime firstWeekday = new DateTime(temp.Year, temp.Month, 1);
//increment to the given day (i.e. if we want the 4th sunday, we must find the first sunday of the month)
while (firstWeekday.DayOfWeek != day)
firstWeekday = firstWeekday.AddDays(1);
//add the number of weeks (note: we already have the first instance, so subtract 1)
firstWeekday = firstWeekday.AddDays(7 * (weeks - 1));
//make sure we haven't gone over to the next month
if (firstWeekday.Month == temp.Month)
results.Add(firstWeekday);
//let's not loop forever ;)
temp = temp.AddMonths(1);
}
return results;
}