Iterate every month with date objects

Question

So I have two ruby Date objects, and I want to iterate them every month. For example if I have Date.new(2008, 12) and Date.new(2009, 3), it would yield me 2008-12, 2009-1, 2009-2, 2009-3 (as Date objects of course). I tried using range, but it yields every day. I saw step method for Date however it only allows me to pass number of days (and each month has different number of those). Anyone have any ideas?

Answer 1

Here is something very Ruby:

first day of each month

(Date.new(2008, 12)..Date.new(2011, 12)).select {|d| d.day == 1}

It will give you an array of the first day for each month within the range.

last day of each month

(Date.new(2008, 12)..Date.new(2012, 01)).select {|d| d.day == 1}.map {|d| d - 1}.drop(1)

Just note that the end date needs to be the month after your end range.

Answer 2

I find that I need to do this sometimes when generating select lists of months. The key is the >> operator on Date, which advances the Date forward one month.

def months_between(start_month, end_month)
  months = []
  ptr = start_month
  while ptr <= end_month do
    months << ptr
    ptr = ptr >> 1
  end
  months
end

results = months_between(Date.new(2008,12), Date.new(2009,3))

Of course, you can format the results however you like in the loop.

months << "#{Date::MONTHNAMES[ptr.month]} #{ptr.year}"

Will return the month name and year ("March 2009"), instead of the Date object. Note that the Date objects returned will be set on the 1st of the month.