week number of the year, kinda

Preferably in ruby, but the logic would be good enough...

I need the week number of the year given that the week is non-standard. So, say you define a week as Sa开发者_如何学JAVAturday -> Friday. Then, given a date, which week number (1-52) is it?

strftime has %U:

> Time.now.strftime('%U')
> => "28"

...but that of course assumes a standard Sunday -> Saturday week.

Use %W instead of %U, it uses Monday as the first day of the week.

Time.now.strftime('%W')

class Date
  def sweek
    date = self + 1
    date.cweek
  end
end

# Today is Sunday, 17 July
Date.today.cweek
#=> 28
Date.today.sweek
#=> 29

Maybe can do like this;

def week_dates( week_num )
    year = Time.now.year
    week_start = Date.commercial( year, week_num, 1 )
    week_end = Date.commercial( year, week_num, 7 )
    week_start.strftime( "%m/%d/%y" ) + ' - ' + week_end.strftime( 
"%m/%d/%y" )
  end

We can figure out how to shift the week number from what's returned by %U (Sun starts the week) by considering this calendar fragment:

August 2015 Su Mo Tu We Th Fr Sa 1 %U => 30 2 3 4 5 6 7 8 %U => 31 9 10 11 12 13 14 15 %U => 32

Let's way we want a Wed-Tue week, abbreviated as format %? (so we don't have to type out "Wed starts week").

We want:

August 2015 We Th Fr Sa Su Mo Tu 1 2 3 4 %? => 30 5 6 7 8 9 10 11 %? => 31 12 13 14 15 %? => 32

Notice how We-Sa stay in the same week number in both systems, while all other days of the week are moved to the previous week in %?.

So we can do this:

startd = Date.new(2015, 8, 1)
# show whole month
pp (startd .. (startd >> 1)-1).map {|d|
  origw = d.strftime('%U').to_i
  # Adjust our new week number if not We-Sa:
  neww = ([3, 4, 5, 6].include?(d.wday) ? origw : origw-1)
  [d.to_s, origw, neww]
}

If you wanted Sat-Fri week, you can subtract 1 for days that aren't Saturday:

d.wday == 6 ? origw : origw-1

Note that there are a couple edge cases, depending on what you choose your week to be (handling these is left as an exercise for the reader). For our Wed-Tue week:

• Year 2014 starts with Wed, but our algorithm puts Jan 1 in week 0 but it should be week 1 (%U puts Jan 1 in week 1 if it's Sunday).
• Year 2007 (and other years that start on Mon or Tue) will cause the days before the first Wed to be in week -1 but they should be week 0.

The more days of the week you're adjusting, the more edge cases you'll have. Sat-Fri week will probably have the most problems because you're adjusting 6 out of 7 days.

If you want a ISO week number use %V according strftime documentation

Example:

require 'date'

puts DateTime.parse('2018-12-30 23:59:59').strftime('%G-%V')
puts DateTime.parse('2018-12-31 00:00:00').strftime('%G-%V')

Result:

2018-52
2019-01

Note that it was used %G for year and not %Y.