Ruby Date Subtraction (e.g. 90 days Ago)
RubyDateRuby Problem Overview
I've been a bit spoiled by the joda-time API of:
DateTime now = new DateTime();
DateTime ninetyDaysAgo = now.minusDays(90);
I'm trying to do a similar thing in Ruby, but I'm
now = Time.now
ninetyDaysAgo = now - (90*24)
However, the math is off here (I'm really working with dates at midnight).
Is there friendly API for date subtraction?
Ruby Solutions
Solution 1 - Ruby
require 'date'
now = Date.today
ninety_days_ago = (now - 90)
Running this thru the IRB console I get:
>>require 'date'
now = Date.today
ninety_days_ago = (now - 90)
require 'date'
=> false
now = Date.today
=> #<Date: 2011-03-02 (4911245/2,0,2299161)>
ninety_days_ago = (now - 90)
=> #<Date: 2010-12-02 (4911065/2,0,2299161)>
If you need the time you could just say now = DateTime.now
Solution 2 - Ruby
For those using Rails, check out the following:
DateTime.now - 10.days
=> Sat, 04 May 2013 12:12:07 +0300
20.days.ago - 10.days
=> Sun, 14 Apr 2013 09:12:13 UTC +00:00
Solution 3 - Ruby
If you're using Rails or don't mind including ActiveSupport, you can use the Numeric#days DSL like this:
ruby-1.9.2-p136 :002 > Date.today
=> Wed, 02 Mar 2011
ruby-1.9.2-p136 :003 > Date.today - 90.days
=> Thu, 02 Dec 2010
Since you are working with dates instead of times, you should also either start with Date instances, or convert your DateTime intances with #to_date. When adding/subtracting numbers from date instances, the numbers are implicitly days.
ruby-1.9.2-p136 :016 > DateTime.now.to_date
=> #<Date: 2011-03-02 (4911245/2,0,2299161)>
ruby-1.9.2-p136 :017 > DateTime.now.to_date - 90
=> #<Date: 2010-12-02 (4911065/2,0,2299161)>
Solution 4 - Ruby
Ruby supports date arithmetic in the Date and DateTime classes, which are part of Ruby's standard library. Both those classes expose #+ and #- methods, which add and subtract days from a date or a time.
$ irb
> require 'date'
=> true
> (DateTime.new(2015,4,1) - 90).to_s # Apr 1, 2015 - 90 days
=> "2015-01-01T00:00:00+00:00"
> (DateTime.new(2015,4,1) - 1).to_s # Apr 1, 2015 - 1 day
=> "2015-03-31T00:00:00+00:00"
Use the #<< and #>> methods to operate on months instead of days. Arithmetic on months is a little different than arithmetic on days. Using Date instead of DateTime makes the effect more obvious.
> (Date.new(2015, 5, 31) << 3).to_s # May 31 - 3 months; 92 days diff
=> "2015-02-28"
Following your joda-time example, you might write something like this in Ruby.
now = DateTime.now
ninety_days_ago = now - 90
or maybe just
ninety_days_ago = DateTime.now - 90
Solution 5 - Ruby
use the number of seconds:
Time.now - 90*24*60*60
Solution 6 - Ruby
This is a super old post, but if you wanted to keep with a Time object, like was originally asked, rather than switching to a Date object you might want to consider using Ruby Facets.
Ruby Facets is a standardized library of extensions for core Ruby classes.
http://rubyworks.github.io/facets/
By requiring Facets you can then do the following with Time objects.
Time.now.less(90, :days)
Solution 7 - Ruby
Simple solution using Rails Active Support:
days90_ago = 90.days.ago.to_date.to_s
OUTPUT:
puts 90_days_ago
=> "2019-10-09" # considering cur_date: 2020-01-07