Create array of months between two dates

Question

I have the following snippet that I use to get the individual dates between two dates:

DateTime[] output = Enumerable.Range(0, 1 + endDate.Subtract(startDate).Days)
    .Select(offset => startDate.AddDays(offset))
    .ToArray(); 

However, the following section

endDate.Subtract(startDate).Days

does not have a .Months to return the months in the date range.

For example, if I provide 1/1/2010 and 6/1/2010 I would expect to return 1/1/2010, 2/1/2010, 3/1/2010, 4/1/2010, 5/1/2010 and 6/1/2010.

Any ideas?

Solution 1

Try this:

static IEnumerable<DateTime> monthsBetween(DateTime d0, DateTime d1)
{
    return Enumerable.Range(0, (d1.Year - d0.Year) * 12 + (d1.Month - d0.Month + 1))
                     .Select(m => new DateTime(d0.Year, d0.Month, 1).AddMonths(m));
}

This includes both the starting month and the ending month. This finds how many months there is, and then creates a new DateTime based on d0´s year and month. That means the months are like yyyy-MM-01. If you want it to includes the time and day of d0 you can replace new DateTime(d0.Year, d0.Month, 1).AddMonths(m) by d0.AddMonths(m).

I see you need an array, in that case you just use monthsBetween(..., ...).ToArray() or put .ToArray() inside the method.

Solution 2

Since I just needed the year and month in between two dates I modified Lasse Espeholt answer a little. suppose: d0 = 2012-11-03

d1 = 2013-02-05

The result will be something like this:

2012-11

2012-12

2013-01

2013-02

 private List<Tuple<int,int>> year_month_Between(DateTime d0, DateTime d1)
    {
        List<DateTime> datemonth= Enumerable.Range(0, (d1.Year - d0.Year) * 12 + (d1.Month - d0.Month + 1))
                         .Select(m => new DateTime(d0.Year, d0.Month, 1).AddMonths(m)).ToList();
     List<Tuple<int, int>> yearmonth= new List<Tuple<int,int>>();

        foreach (DateTime x in datemonth)
        {
            yearmonth.Add(new Tuple<int, int>(x.Year, x.Month));
        }
        return yearmonth;
    }

Solution 3

Is this what you are looking for? The requirement is very ambiguous.

DateTime[] calendarMonthBoundaries = Enumerable.Range(0, 1 + endDate.Subtract(startDate).Days)
    .Select(offset => startDate.AddDays(offset))
    .Where(date => date.Day == 1)
    .ToArray();

Solution 4

You could enumerate increments of months with:

private static IEnumerable<DateTime> ByMonths(DateTime startDate, DateTime endDate)
{
  DateTime cur = startDate;

  for(int i = 0; cur <= endDate; cur = startDate.AddMonths(++i))
  {
    yield return cur;
  }
}

and then call ToArray() on that if you want an array. It's reasonably good about having values that are likely to be what is wanted; e.g. if you start at Jan 31^st you'll next get Feb 28^th (or 29^th on leap years), then Mar 31^st, then Apr 30^th and so on.

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Comments

[Dave Lucre]

DateTime[] months = ByMonths({30/01/2013 12:00:00 AM}, {4/04/2013 12:00:00 AM}).ToArray(); This only returns 3 months (jan, feb, mar), April is missing.

[Jon Hanna]

@DaveLucre I'm not sure that's a bad thing, because I'm not sure just what the requirement in the question is considering "between". It could certainly be amended to include April in that case, I just don't know if it should.

[Rudean]

I actually like how simple this solution is! Just analyze all dates between start date and end date, but return only start month dates. Probably not the quickest solution but pretty straightforward.

[Rudean]

And if you want to get not months, but years, you can do it like this Enumerable.Range(0, (d1.Year - d0.Year) + 1) .Select(m => new DateTime(d0.Year, 1, 1).AddYears(m))