# Finding the date of an event based on related events

Hi all,

I’m doing some planning to write a simple utility program for
maintaining my schedule. The basic scenario is that, in my job, I have
a series of multi-stage procedures to perform, and for each instance
of the procedure, the stages need to happen a fixed number of business
days apart (i.e, if step one happens on Monday, step two is Friday,
but if step one is Tuesday, step two will be the following Monday). As
one of the first steps of the program, I’m going to write a script to
quickly spit out the calendar dates of all steps given the date of the
first and the relative date (in business days) of all the others.

My question is, can you help me drum up a ‘smart’ way to take weekends
and holidays into account? I know that with Ruby’s Date class you can
use the - (minus) operator to subtract x days from the date of an
existing event. which is how I can find the exact date once I’ve
determined the number of total days it will be before it has been x

But the “human” solution to the problem isn’t very efficient -
iterating over the days with a counter, checking Date.wday, ignoring
days that return 0 and 6, and spitting back the date at which the
counter reaches x. I’d like to find a more elegant and computationally
efficient solution.

If you’ve worked out this problem before, or a better solution seems
readily available to you, I’d love input. If my explanation was

-Andrew Fallows

Kaldrenon wrote:

Hi all,

I’m doing some planning to write a simple utility program for
maintaining my schedule. The basic scenario is that, in my job, I have
a series of multi-stage procedures to perform, and for each instance
of the procedure, the stages need to happen a fixed number of business
days apart (i.e, if step one happens on Monday, step two is Friday,
but if step one is Tuesday, step two will be the following Monday). As
one of the first steps of the program, I’m going to write a script to
quickly spit out the calendar dates of all steps given the date of the
first and the relative date (in business days) of all the others.

My question is, can you help me drum up a ‘smart’ way to take weekends
and holidays into account?
(…)

-Andrew Fallows

To exclude just the weekends you could do

class Date
end
end

Which returns a new Date and seems to work with negative n’s. (Just
wrote this code, don’t know if it’s bullet proof).

Holidays are a complication.Ideally the solution would allow for
different holidays for different countries. Working hours could be
specified, to enable calculating exactly when a 14 hour job starting on
friday 24 december 15:15 in the US would finish.

Two applications I work with have these features. I’m not aware of a
ruby solution/gem.

Regards,

Siep

On Fri, Jul 18, 2008 at 5:04 PM, Siep K. [email protected]
wrote:

wrote this code, don’t know if it’s bullet proof).
It isn’t. It won’t work if you start from a weekend day.

Use today (Saturday), and do

puts d

=> 2008-07-28

I like the approach, though.

Todd

-------- Original-Nachricht --------

Datum: Sat, 19 Jul 2008 01:20:12 +0900
Von: Kaldrenon [email protected]
An: [email protected]
Betreff: Finding the date of an event based on related events.

first and the relative date (in business days) of all the others.
days that return 0 and 6, and spitting back the date at which the
counter reaches x. I’d like to find a more elegant and computationally
efficient solution.

If you’ve worked out this problem before, or a better solution seems
readily available to you, I’d love input. If my explanation was

-Andrew Fallows

Dear Andrew,

reading previous responses to your post, I’d like to mention that you
can get a list of public holidays from the Wikipedia

for many countries, the movable holidays are mostly Easter and
Pentecost,
there is a listing of the Easter dates here (and Pentecost is, I
believe, just 7 weeks later):

http://www.assa.org.au/edm.html#List20

and, secondly, that for the main task you have – scheduling — you
could use a “Constraint Programming” framework,
such as this:

http://gecoder.rubyforge.org/

where you input all the conditions you have and get back a solution…

Best regards,

Axel

On Sat, Jul 19, 2008 at 1:13 PM, Todd B. [email protected]
wrote:

w_days = [nil] + (Date.today…Date.today +
some_number_of_days).map.select {|day| (day.cwday / 5).zero?}

That should be a 6 not a 5.

Todd

On Fri, Jul 18, 2008 at 11:20 AM, Kaldrenon [email protected] wrote:

first and the relative date (in business days) of all the others.
days that return 0 and 6, and spitting back the date at which the
counter reaches x. I’d like to find a more elegant and computationally
efficient solution.

If you’ve worked out this problem before, or a better solution seems
readily available to you, I’d love input. If my explanation was

-Andrew Fallows

Maybe build a calendar beforehand that only includes work days…

w_days = [nil] + (Date.today…Date.today +
some_number_of_days).map.select {|day| (day.cwday / 5).zero?}

…and then later…

w_days -= holiday_dates #which is an array of holiday Date objects
chosen by you

…which afterwards you could walk through 6 at a time.

That, to me is somewhat elegant and robust, but Siep’s idea will work
if the script/program will always run from a weekday. You will notice
the peculiarity that Saturday acts like Monday and Sunday acts like
Tuesday with Siep’s example.

I’d probably create a WorkCalendar class, though.

Todd

Following error message:
===> Patching for ruby18-gems-1.2.0
===> ruby18-gems-1.2.0 depends on file: /usr/local/bin/ruby18 - found
===> Applying FreeBSD patches for ruby18-gems-1.2.0
=> Patch patch-lib-rubygems-source_info_cache.rb failed to apply
cleanly.
*** Error code 1

Stop in /usr/ports/devel/ruby-gems

FreeBSD ***.vizion2000.net 7.0-STABLE FreeBSD 7.0-STABLE #0: Wed Jul 16
09:27:38 PDT 2008 @***.vizion2000.net:/usr/obj/usr/src/sys/GENERIC
amd64

This system has just been upgraded from 6.3 to 7.0-Stable. Is there a
possible connection here?

After getting this error I checked to make sure the port tree was
uptofate
and tried again with the same result.
I am currently recompiling ruby* ports on the system after a portsclean
with:
Has anyone else experienced a similar problem?
I will report result of recompile when it finishes.

David

===> Patching for ruby18-gems-1.2.0
09:27:38 PDT 2008
Has anyone else experienced a similar problem?
I will report result of recompile when it finishes.

David

The recompile produced the same result for ruby-gems.
Is a pr needed here or is someone on to it already?
David

On Jul 19, 2:08 pm, Todd B. [email protected] wrote:

That, to me is somewhat elegant and robust, but Siep’s idea will work
if the script/program will always run from a weekday.

The general idea is that it will, given that the input will always be
an event that the user is scheduling, and the context is scheduling
for a M-F 5-day workweek setting. However, in the interest of
versatility, I like to avoid coding in a “assuming the user knows what
format to input” setup.

Thanks to all for the replies and advice! This is kind of a side
project for me at the moment, so I haven’t yet gotten a chance to
implement any of these things or test them, but I will be sure to get
back to the group with my results when I do.

As for my holiday list, I think the simplest initial concept, for
testing the basic functionality, is a Hash of Date objects based on my
employer’s list of holidays for which employees get time off, as
opposed to a list of all US holidays, but I’ll look into a flexible
way to plug in a holiday list at a later point.

Thanks again,
Andrew