From: Rick DeNatale <rick.denatale@...>
Date: 2008-02-29T23:32:14+09:00
Subject: Re: Getting number of days in a month -- getting the number of weeks in a year.

On 2/29/08, Siep Korteling <s.korteling@gmail.com> wrote:
> Rick Denatale wrote:
>  > On 2/28/08, Serg Koren <skoren@comcast.net> wrote:
>
> > (...)
>
> > a normal year starting on weekday 1 starts with 52 full weeks and ends
>  > with a 'week' of 1 days a total of 53 'weeks.'
>  > a leap year starting on weekday 1 starts with 52 full weeks and ends
>  > with a 'week' of 2 days a total of 53 'weeks.'
>  >
>
> (...)
>
>  Following this analysis:
>
>  require 'date'
>
>  def numweeks(year)
>   start_year = Date.civil(year,1,1)
>   end_year = Date.civil(year,-1,-1)
>   (start_year.strftime("%U") .. end_year.strftime("%U")).to_a.size
>  end
>
>  puts numweeks(2028)   # =>54
>

Well, that doesn't exactly follow my analysis, but it does work, but
only if you define the week to start on Sunday.

Another way which DOES follow my analysis

 def leap?(year)
     year % 400 == 0 || year % 4 == 0 && year % 100 != 0
 end

 def numweeks(year, start_wday = 0)
      leap?(year) && Date.civil(year,1,2).wday == start_wday ? 54 : 53
 end

As it turns out, rather unsurprisingly given the world in which we
live,  numbering the weeks in a year is more complicated than counting
them.

http://en.wikipedia.org/wiki/Week#Week_number
http://en.wikipedia.org/wiki/ISO_week_date
-- 
Rick DeNatale

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