From: Rick DeNatale <rick.denatale@...>
Date: 2007-03-16T04:28:16+09:00
Subject: Re: Calculating the age given DOB

I think that this does the right thing:

rick@frodo:/public/rubyscripts$ cat datemath.rb
#!/usr/math/bin/ruby


require 'date'
class Date

  # return the number of days since the beginning of the year
  def years_since(date)
    # The parens in the expression below aren't strictly necessary, but
    # I think it makes what's going on a little bit clearer.
    first, last = *(self >= date ? [date, self] : [self, date])
    (self <=> date) * ((last.year - first.year) - (first.yday >
last.yday ? 1 : 0))
  end
end

def tryit(d1,d2)
  puts "There are #{d1.years_since(d2)} years between #{d2} and #{d1}"
end

tryit(Date.new(2007,3,15), Date.new(2000,3,14))
tryit(Date.new(2000,3,14), Date.new(2007,3,15))
tryit(Date.new(2007,3,15), Date.new(2000,3,15))
tryit(Date.new(2007,3,15), Date.new(2000,3,16))
tryit(Date.new(2000,3,16), Date.new(2007,3,15))

tryit(Date.new(2007,2,27), Date.new(2000,2,29))
tryit(Date.new(2000,2,29), Date.new(2000,2,27))
tryit(Date.new(2007,2,28), Date.new(2000,2,29))
tryit(Date.new(2000,2,29), Date.new(2007,2,28))
tryit(Date.new(2000,2,29), Date.new(2007,3,1))
tryit(Date.new(2007,3,1), Date.new(2000,2,29))
tryit(Date.new(2007,3,2), Date.new(2000,2,29))
tryit(Date.new(2000,2,29), Date.new(2007,3,2))

rick@frodo:/public/rubyscripts$ ruby datemath.rb
There are 7 years between 2000-03-14 and 2007-03-15
There are -7 years between 2007-03-15 and 2000-03-14
There are 6 years between 2000-03-15 and 2007-03-15
There are 6 years between 2000-03-16 and 2007-03-15
There are -6 years between 2007-03-15 and 2000-03-16
There are 6 years between 2000-02-29 and 2007-02-27
There are 0 years between 2000-02-27 and 2000-02-29
There are 6 years between 2000-02-29 and 2007-02-28
There are -6 years between 2007-02-28 and 2000-02-29
There are -7 years between 2007-03-01 and 2000-02-29
There are 7 years between 2000-02-29 and 2007-03-01
There are 7 years between 2000-02-29 and 2007-03-02
There are -7 years between 2007-03-02 and 2000-02-29


-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/