We Keep Coding

Calculate exact no of week for date range

A person is engaged in different works in different time duration which will start from Monday and end on friday as follows.Monday to Friday will be considered as 1 week.Any overlapping weeks be considered as 1 week.
Below are the scenario
"AssignedEngagementdate":[
{"Startdate":"01/03/2022","Enddate":"01/07/2022"},
{"Startdate":"01/10/2022","Enddate":"01/14/2022"},
{"Startdate":"01/10/2022","Enddate":"01/21/2022"},
{"Startdate":"02/14/2022","Enddate":"02/18/2022"}
]
Here I need to find the no of weeks assigned by this person and it should be 4 since one week is from 10th Jan to 14 Feb is overlapping in 2 engagement.
How I can do this in C# using linq. I was trying to fetch min start date and max end date from list and find the difference and converting in no of weeks but it has not given the actual result since date assigned is not consistent.

The trick is to convert each date range into an enumerated week range, or at least a list of distinct dates (such as Sundays) corresponding to each week or partial week. SelectMany() lets you gather them all together, after which a distinct count gives you an answer.
Try something like:
int numberOfWeeks = AssignedEngagementdate
.SelectMany(a => {
DateTime firstSunday = a.Startdate.AddDays(-(int)a.Startdate.DayOfWeek);
DateTime lastSunday = a.Enddate.AddDays(-(int)a.Enddate.DayOfWeek); // May be same as firstSunday
int weeks = (lastSunday - firstSunday).Days / 7 + 1;
// Enumerate one Sunday per week
return Enumerable.Range(0, weeks).Select(i => firstSunday.AddDays(7 * i));
})
.Distinct()
.Count();
You may still need to consider and test cases where assignments start or end on days other than Monday and Friday. The above should handle most such cases.

Without linq, you can try this Datetime extension :
public static int NumberOfWeeksBetween(this DateTime start, DateTime end)
{
TimeSpan span = end.Subtract(start);
if (span.Days <= 7)
{
if (start.DayOfWeek > end.DayOfWeek) return 2;
else return 1;
}
int days = span.Days - 7 + (int)start.DayOfWeek;
int weekCount = 1;
int dayCount = 0;
for (weekCount = 1; dayCount < days; weekCount++) dayCount += 7;
return weekCount;
}

Is this a good algorithm to find each week in a given month?

I need to take a month (defined as a start and end date) and return a set of date ranges for each week in that month. A week is defined as Sunday through Saturday. A good way to visualize it is if you double click on your Windows date in the start bar:
The month of October 2011 has 6 weeks: 10/1-10/1, 10/2-10/8, 10/9-10/15, 10/16-10/22, 10/23-10/29 and 10/30-10/31.
I can describe each week as a struct:
struct Range
{
public DateTime Start;
public DateTime End;
public Range(DateTime start, DateTime end)
{
Start = start;
End = end;
}
}
I need to write a function that takes a month and returns an array of ranges within it. Here's my first attempt, which appears to work and addresses the obvious edge cases:
public static IEnumerable<Range> GetRange(DateTime start, DateTime end)
{
DateTime curStart = start;
DateTime curPtr = start;
do
{
if (curPtr.DayOfWeek == DayOfWeek.Saturday)
{
yield return new Range(curStart, curPtr);
curStart = curPtr.AddDays(1);
}
curPtr = curPtr.AddDays(1);
} while (curPtr <= end);
if(curStart <= end)
yield return new Range(curStart, end);
}
I would like to know if there's a cleaner or more obvious approach to do the same. I'm not overly concerned about performance, but I'd like to improve code readability and make the algorithm a bit more concise. Perhaps there's a very creative solution involving a single LINQ expression or something. Thanks!

This is based on simply incrementing by 7, as suggested by Previti, ready for international use. If your C# is < 4.0, remove the default parameter = DayOfWeek.Sunday
public static IEnumerable<Range> GetRange(DateTime start, DateTime end, DayOfWeek startOfTheWeek = DayOfWeek.Sunday)
{
if (start > end)
{
throw new ArgumentException();
}
// We "round" the dates to the beginning of the day each
start = start.Date;
end = end.Date;
// The first week. It could be "shorter" than normal. We return it "manually" here
// The 6 + startOfWeek - start.DayOfWeek will give us the number of days that you
// have to add to complete the week. It's mod 7. It's based on the idea that
// the starting day of the week is a parameter.
DateTime curDay = new DateTime(Math.Min(start.AddDays((6 + (int)startOfTheWeek - (int)start.DayOfWeek) % 7).Ticks, end.Ticks), start.Kind);
yield return new Range(start, curDay);
curDay = curDay.AddDays(1);
while (curDay <= end)
{
// Each time we add 7 (SIX) days. This is because the difference between
// as considered by the problem, it's only 6 * 24 hours (because the week
// doesn't end at 23:59:59 of the last day, but at the beginning of that day)
DateTime nextDay = new DateTime(Math.Min(curDay.AddDays(6).Ticks, end.Ticks), start.Kind);
yield return new Range(curDay, nextDay);
// The start of the next week
curDay = nextDay.AddDays(1);
}
}
Some small notes: Math.Min isn't defined for DateTime, so I cheat a little by taking the Ticks of the DateTimes and comparing them. Then I rebuild the DateTime. I always use the DateTimeKind of the start date.
When you debug yield code, remember to "materialize" the result through the use of ToList or ToArray, otherwise the code won't be executed :-)

Calculate Monday-Sunday week from a DateTime object

I'm trying to write a method that will return a list of DateTimes representing a Monday-Sunday week. Its supposed to take the DateTime given to it and use it to calculate the surrounding dates
It calculates the starting date ok but the problem begins when it hits the last loop. With each run through the DateTime variable tmpDate should be incremented by 1 day, then added to the list. However, as it stands I'm getting back a List containing 7 starting dates.
Can anyone see where I'm going wrong (I have the feeling I may be made to look like a bit of a simpleton on this :) )?
Also, apologies if this is an often-asked question. Could see plenty of Start date/End Date and week number type questions, but none specifically dealing with this type of problem.
private List<DateTime> getWeek(DateTime enteredDate)
{
/* Create List to hold the dates */
List<DateTime> week = new List<DateTime>();
int enteredDatePosition = (int)enteredDate.DayOfWeek;
/* Determine first day of the week */
int difference = 0;
for (int i = 0; i < 7; i++)
{
difference++;
if (i == enteredDatePosition)
{
break;
}
}
// 2 subtracted from difference so first and enteredDatePostion elements will not be counted.
difference -= 2;
DateTime startDate = enteredDate.Subtract(new TimeSpan(difference, 0, 0, 0));
week.Add(startDate);
/* Loop through length of a week, incrementing date & adding to list with each iteration */
DateTime tmpDate = startDate;
for (int i = 1; i < 7; i++)
{
tmpDate.Add(new TimeSpan(1, 0, 0, 0));
week.Add(tmpDate);
}
return week;
}

DateTimes are immutable.
tmpDate.Add(...) returns a new DateTime, and does not modify tmpDate.
You should write tmpDate = tmpDate.AddDays(1) or tmpDate += TimeSpan.FromDays(1)

I believe this snippet is tailored towards Sunday trough Saturday, but you can try something like this:
DateTime ToDate = DateTime.Now.AddDays((6 - (int)DateTime.Now.DayOfWeek) - 7);
DateTime FromDate = ToDate.AddDays(-6);

You're making your algorithm more complex than it needs to be. Check out this working snippet:
using System;
using System.Collections.Generic;
public class MyClass
{
public static void Main()
{
// client code with semi-arbitrary DateTime suuplied
List<DateTime> week = GetWeek(DateTime.Today.AddDays(-2));
foreach (DateTime dt in week) Console.WriteLine(dt);
}
public static List<DateTime> GetWeek(DateTime initDt)
{
// walk back from supplied date until we get Monday and make
// that the initial day
while (initDt.DayOfWeek != DayOfWeek.Monday)
initDt = initDt.AddDays(-1.0);
List<DateTime> week = new List<DateTime>();
// now enter the initial day into the collection and increment
// and repeat seven total times to get the full week
for (int i=0; i<7; i++)
{
week.Add(initDt);
initDt = initDt.AddDays(1.0);
}
return week;
}
}

Calculate StartDate when End Date & back days given

I am developing c#.net solution where i have to calculate Start Date based on provided End date and Duration (back days) without weekends.
i.e. End Date: 05/5/2011
Back days: 5
Start Date = (05/5/2011) - 5 days (Excludes weekends)
Start Date = 29/04/2011
thanks you,

Something like this is probably what I'd do:
DateTime CalcStartDate(DateTime endTime, int daysBack)
{
DateTime startTime = endTime.Date;
while (daysBack > 0)
{
startTime = startTime.AddDays(-1);
if (startTime.DayOfWeek != DayOfWeek.Saturday && startTime.DayOfWeek != DayOfWeek.Sunday)
{
--daysBack;
}
}
return startTime;
}
Or even better, Bala's suggestion of using a library. Date and time is messy, a hardened/tested library is usually a good choice.

Bala R has the answer correctly. Here is a link to an article on how to use the AddBusinessDays() method:
http://www.codeproject.com/KB/cs/AddBusinessDay.aspx

I don't know how far back you are going to go. If it is a lot of days back then looping through the days might be a little CPU intensive. Well, probably not with modern processors...
I decided to implement a solution without a loop.
My code is a little more difficult to read, but it should be more efficient performance-wise.
public static class DateTimeExtensions
{
public static DateTime SubtractBusinessDays(this DateTime fromDateTime, int days)
{
var subtractDays = days % 5;
var dayNumber = fromDateTime.DayOfWeek == DayOfWeek.Sunday ? 7 : (int)fromDateTime.DayOfWeek;
var addDays = Math.Max(dayNumber - 5, 0);
var result = fromDateTime.AddDays(addDays - subtractDays - (days / 5 * 7));
if ((addDays + dayNumber) % 7 <= subtractDays)
result = result.AddDays(-2);
return result;
}
}

How can I get correct payperiod from date?

I feel like this is math problem more than anything. My company has employees all over the country. Some parts of the company are on an "odd" pay cycle and some are on "even". I call the starting date of a given pay period a "payperiod". I need to do two things:
1) determine the payperiod in which a given date falls
//Something like this:
public static DateTime getPayPeriodStartDate(DateTime givenDate, string EvenOrOdd)
{ .. }
2) get a list of payperiods between two dates:
//Something like this:
public static List<DateTime> getPayPeriodsBetween(DateTime start, DateTime end, string EvenOrOdd)
{ .. }
I'm using a couple dates as fixed standards on which to base any future pay period dates. The fixed standard dates for even and odd are as follows:
Even - 01/04/09
Odd - 01/11/09
Each pay period starts on the sunday of the week and goes for two weeks. For instance, using the standard dates above, the first even pay period starts on 01/04/09 and ends on 01/17/09. The first odd pay period starts on 01/11/09 and ends on 01/24/09. As you can see, there is some overlap. We have thousands of employees so it's necessary to split them up a bit.
I have a solution that is based on week numbers but it's clunky and has to be "fixed" every new year. I'm wondering how you would handle this.

Not fully optimized or tested, but this is what I came up with:
const int DaysInPeriod = 14;
static IEnumerable<DateTime> GetPayPeriodsInRange(DateTime start, DateTime end, bool isOdd)
{
var epoch = isOdd ? new DateTime(2009, 11, 1) : new DateTime(2009, 4, 1);
var periodsTilStart = Math.Floor(((start - epoch).TotalDays) / DaysInPeriod);
var next = epoch.AddDays(periodsTilStart * DaysInPeriod);
if (next < start) next = next.AddDays(DaysInPeriod);
while (next <= end)
{
yield return next;
next = next.AddDays(DaysInPeriod);
}
yield break;
}
static DateTime GetPayPeriodStartDate(DateTime givenDate, bool isOdd)
{
var candidatePeriods = GetPayPeriodsInRange(givenDate.AddDays(-DaysInPeriod), givenDate.AddDays(DaysInPeriod), isOdd);
var period = from p in candidatePeriods where (p <= givenDate) && (givenDate < p.AddDays(DaysInPeriod)) select p;
return period.First();
}

I haven't tested for many test cases, but I think this fits the bill:
public static DateTime getPayPeriodStartDate(DateTime givenDate, string EvenOrOdd)
{
DateTime newYearsDay = new DateTime(DateTime.Today.Year, 1, 1);
DateTime firstEvenMonday = newYearsDay.AddDays((8 - (int)newYearsDay.DayOfWeek) % 7);
DateTime firstOddMonday = firstEvenMonday.AddDays(7);
TimeSpan span = givenDate - (EvenOrOdd.Equals("Even") ? firstEvenMonday : firstOddMonday);
int numberOfPayPeriodsPast = span.Days / 14;
return (EvenOrOdd.Equals("Even") ? firstEvenMonday : firstOddMonday).AddDays(14 * numberOfPayPeriodsPast);
}
public static List<DateTime> getPayPeriodsBetween(DateTime start, DateTime end, string EvenOrOdd)
{
DateTime currentPayPeriod = getPayPeriodStartDate(start, EvenOrOdd);
if (currentPayPeriod < start) currentPayPeriod = currentPayPeriod.AddDays(14);
List<DateTime> dtList = new List<DateTime>();
while (currentPayPeriod <= end)
{
dtList.Add(currentPayPeriod);
currentPayPeriod = currentPayPeriod.AddDays(14);
}
return dtList;
}
I am sure it can be improved.

I had a need to do something similar and was able to do it very easily using LINQ. Simply build up a List for even and odd and then query between dates from the odd/even as necessary. Also, I recommend you move to an emum for parameters like EvenOrOdd where you have fixed values.

I had a similar problem a few months ago, and I ended up writing a quick script to create entries in a database for each pay period so I never had to actually do the math. This way, The system works the same speed, and doesn't have to do any slow iterations every time a period is requested.
That being said, you can always take the starting date, and add two weeks (or however long your periods are) over and over until you reach the dates you specify in the function call. This is a bit ugly, and the longer it sits in production, the slower it gets (since the dates are getting further and further apart).
Both ways are trivial to implement, it's just a matter of what kind of resources you have at hand to tackle the issue.
So, for number 1: Start with either 1/4/2009 or 1/11/2009 (depending on even/odd pay week) and add 2 weeks until the givenDate is less than the date you're testing + 2 weeks. That's the start of the period.
For number 2: Same thing, start at the date and add 2 weeks until you're within the date range. While you're there, add each item to a list. As soon as you're past the last date, break out of your loop and return your shiny new list.
If you used my method and went with a database to house all this info, it turns into 2 simple queries:
1)SELECT * FROM payperiods WHERE startdate<=givenDate ORDER BY startdate LIMIT 1
2) SELECT * FROM payperiods WHERE startdate>=givenDate AND enddate<=givenDate ORDER BY startdate

It works perfectly. I have tested.
public static DateTime GetFirstDayOfWeek(DateTime dayInWeek)
{
CultureInfo _culture = (CultureInfo)CultureInfo.CurrentCulture.Clone();
CultureInfo _uiculture = (CultureInfo)CultureInfo.CurrentUICulture.Clone();
_culture.DateTimeFormat.FirstDayOfWeek = DayOfWeek.Monday;
_uiculture.DateTimeFormat.FirstDayOfWeek = DayOfWeek.Monday;
System.Threading.Thread.CurrentThread.CurrentCulture = _culture;
System.Threading.Thread.CurrentThread.CurrentUICulture = _uiculture;
// CultureInfo defaultCultureInfo = CultureInfo.CurrentCulture;
DayOfWeek firstDay = _culture.DateTimeFormat.FirstDayOfWeek;
DateTime firstDayInWeek = dayInWeek.Date;
// Logic Of getting pay period Monday(Odd monday)
int i = Convert.ToInt32(firstDay);
while (firstDayInWeek.DayOfWeek != firstDay)
if (i % 2 != 0)
{ firstDayInWeek = firstDayInWeek.AddDays(-1); }
else
{
firstDayInWeek = firstDayInWeek.AddDays(-2);
}
return firstDayInWeek;
}