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?

Answer 1

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();

Answer 2

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.

Answer 3

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.