Handling week numbers according to US Standard and ISO 8601

Hi ruby-lang list,

Thank you all for reading this mail.

I am struggling to handle week numbers properly on a web platform made
in
Ruby that is used across several countries. I have googled this for days
trying to find a solution, but I have not had any success whatsoever so
far.

The problem is the following:

------- DENMARK:

  1. Say we are using the system in Denmark and we want to know the week
    number of the date 2009-12-31.

  2. Denmark follows the ISO 8601 standard for calendar handling, and the
    server running the system is initialized using the Europe/Copenhagen
    time
    zone.

  3. Executing Date.civil(2009, 12, 31).cweek returns “53”, which is the
    correct answer, since December 31st 2009 is part of week 53 in Denmark
    (and
    the rest of Europe, pretty much).

------- USA:

  1. Now we are using the system in USA, but still communicating with the
    same
    server here in Denmark, the UI itself just speaks English.

  2. When I execute Date.civil(2009, 12, 31).cweek, it still - obviously -
    returns “53”. But in the case of USA, this is wrong, since December 31st
    2009 would be week 52 according to the US Standard.


Now, I have tried to use TZInfo for Ruby, doing a
Time.zone.parse(“2009-12-31”).strftime("%W") to get the week number of
December 31st 2009 - with weeks beginning on Monday (ISO 8601). This
returns
52, which is WRONG according to European standards.

However, executing Time.zone.parse(“2009-12-31”).strftime("%U") to get
the
week number of December 31st 2009 - with weeks beginning on Sunday (US
Standard) - returns 52. Which is right.

So, I have Date.civil that tells me one thing - 53 - and Time.zone that
tells me another - 52. Either is wrong in one of the cases.

Do you guys have any ideas regarding handling the week numbers correctly
according to the country of the user? Is there a way to tell
Date.civil() to
follow a specific standard, or does it just inherit from the machine
settings no matter what? What can I do to fix this?

Thank you for your help.

All the best,
Kasper T.
[email protected]

On Wed, Apr 28, 2010 at 4:58 PM, Kasper T. [email protected]
wrote:

------- DENMARK:
the rest of Europe, pretty much).

So, I have Date.civil that tells me one thing - 53 - and Time.zone that
Kasper T.
[email protected]

My ri_cal gem (whose purpose is to support rfc2445/5545 icalendar
data) extends Time and DateTime with this method

    # return the iso year of the receiver
    # == parameter
    # wkst:: an integer representing the day of the week on which

weeks are deemed to start. This uses
# the ruby convention where 0 represents Sunday.
def iso_year(wkst)

http://github.com/rubyredrick/ri_cal

Rick DeNatale

Blog: http://talklikeaduck.denhaven2.com/
Github: http://github.com/rubyredrick
Twitter: @RickDeNatale
WWR: http://www.workingwithrails.com/person/9021-rick-denatale
LinkedIn: http://www.linkedin.com/in/rickdenatale

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