algorithm to truncate date to beginning of week?
in [Ruby]
|
From: Gary Wright on 9 Feb 2010 13:53 On Feb 9, 2010, at 1:32 PM, Chuck Remes wrote: > I need to be able to take any date after Jan 1, 1980 and truncate it to the nearest week. > > Example: > > Wed Jan 09 17:53:23 -0600 1980 should truncate to Sun Jan 06 00:00:00 -0600 1980 > > Tue Feb 09 12:29:51 -0600 2010 should truncate to Sun Feb 07 00:00:00 -0600 2010 > > I've tried all sorts of tricks with modulus (% operator) on the integer representation of time but I can't get anything to work over a range of dates. > > Anyone have any bright ideas? >> require 'active_support' => true >> Time.now.beginning_of_week => Mon Feb 08 00:00:00 -0500 2010 >> It also looks like midnight is considered part of the next day not the previous day as in your example. Gary Wright
From: Yossef Mendelssohn on 9 Feb 2010 13:58 On Feb 9, 12:32 pm, Chuck Remes <cremes.devl...(a)mac.com> wrote: > My end goal is to always be able to pick the first Sunday at midnight backwards from a given date. If there is another approach to accomplish this, please share. Use the logic inherent in Date objects. They can tell you the weekday (as an integer, 0-based starting at Sunday), and subtraction/addition work on days. $ irb -rdate >> d = Date.today => #<Date: 4910473/2,0,2299161> >> d.to_s => "2010-02-09" >> d-d.wday => #<Date: 4910469/2,0,2299161> >> _.to_s => "2010-02-07" A Date object is just that, a date. If you mean a time, you can recreate the date using parts of the time. >> t = Time.now => Tue Feb 09 12:54:48 -0600 2010 >> d = Date.new(t.year, t.month, t.day) => #<Date: 4910473/2,0,2299161> >> d.to_s => "2010-02-09" Or if you still need a Time object when you're done, you can go the other way as well. >> t = Time.local(d.year, d.month, d.day) => Tue Feb 09 00:00:00 -0600 2010 HTH HAND -- -yossef
From: Yossef Mendelssohn on 9 Feb 2010 14:01 On Feb 9, 12:53 pm, Gary Wright <gwtm...(a)mac.com> wrote: > On Feb 9, 2010, at 1:32 PM, Chuck Remes wrote: > > Anyone have any bright ideas? > >> require 'active_support' > => true > >> Time.now.beginning_of_week > > => Mon Feb 08 00:00:00 -0500 2010 > > > > It also looks like midnight is considered part of the next day not the previous day as in your example. No, ActiveSupport just thinks Monday is the beginning of the week. http://api.rubyonrails.org/classes/ActiveSupport/CoreExtensions/Time/Calculations.html#M001151 -- -yossef
From: Rick DeNatale on 9 Feb 2010 14:12 On Tue, Feb 9, 2010 at 1:53 PM, Gary Wright <gwtmp01(a)mac.com> wrote: > > On Feb 9, 2010, at 1:32 PM, Chuck Remes wrote: > >> I need to be able to take any date after Jan 1, 1980 and truncate it to the nearest week. >> >> Example: >> >> Wed Jan 09 17:53:23 -0600 1980 should truncate to Sun Jan 06 00:00:00 -0600 1980 >> >> Tue Feb 09 12:29:51 -0600 2010 should truncate to Sun Feb 07 00:00:00 -0600 2010 >> >> I've tried all sorts of tricks with modulus (% operator) on the integer representation of time but I can't get anything to work over a range of dates. >> >> Anyone have any bright ideas? > >>> require 'active_support' > => true >>> Time.now.beginning_of_week > => Mon Feb 08 00:00:00 -0500 2010 >>> > > It also looks like midnight is considered part of the next day not the previous day as in your example. No, actually ActiveSupport defines the week to start on Monday, which is the ISO 8601 definition, not Sunday. To get the beginning of a Sunday starting week using ActiveSupport, you could use Time.now.end_of_week.beginning_of_day This will get the end of the next Sunday on or after the time in question, and then adjust to the beginning of the day. Approaches like Time.now.beginning_of_week - 1.day will fail on Sundays, you'll get the previous Sunday instead. -- Rick DeNatale Blog: http://talklikeaduck.denhaven2.com/ Twitter: http://twitter.com/RickDeNatale WWR: http://www.workingwithrails.com/person/9021-rick-denatale LinkedIn: http://www.linkedin.com/in/rickdenatale
From: Chuck Remes on 9 Feb 2010 14:21 On Feb 9, 2010, at 12:58 PM, Yossef Mendelssohn wrote: > On Feb 9, 12:32 pm, Chuck Remes <cremes.devl...(a)mac.com> wrote: >> My end goal is to always be able to pick the first Sunday at midnight backwards from a given date. If there is another approach to accomplish this, please share. > > Use the logic inherent in Date objects. They can tell you the weekday > (as an integer, 0-based starting at Sunday), and subtraction/addition > work on days. > > $ irb -rdate >>> d = Date.today > => #<Date: 4910473/2,0,2299161> >>> d.to_s > => "2010-02-09" >>> d-d.wday > => #<Date: 4910469/2,0,2299161> >>> _.to_s > => "2010-02-07" Ah! Date#wday is what I needed! I do need Time objects but it's easy (as you pointed out) to convert between them. Thanks for your insight. cr
|
Next
|
Last
Pages: 1 2 Prev: [Q] algorithm to truncate date to beginning of week? Next: Ray Tracing API. |