From: Chuck Remes <cremes.devlist@...>
Date: 2010-02-10T04:21:34+09:00
Subject: Re: algorithm to truncate date to beginning of week?


On Feb 9, 2010, at 12:58 PM, Yossef Mendelssohn wrote:

> On Feb 9, 12:32 pm, Chuck Remes <cremes.devl...@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