How to round a time down to the nearest 15 minutes in Ruby?

Question

Is there an easy way to round a Time down to the nearest 15 minutes?

This is what I'm currently doing. Is there an easier way to do it?

t = Time.new rounded_t = Time.local(t.year, t.month, t.day, t.hour, t.min/15*15) 

Answer 1

You said "round down", so I'm not sure if you're actually looking for the round or the floor, but here's the code to do both. I think something like this reads really well if you add round_off and floor methods to the Time class. The added benefit is that you can more easily round by any time partition.

require 'active_support/core_ext/numeric' # from gem 'activesupport'  class Time   # Time#round already exists with different meaning in Ruby 1.9   def round_off(seconds = 60)     Time.at((self.to_f / seconds).round * seconds).utc   end    def floor(seconds = 60)     Time.at((self.to_f / seconds).floor * seconds).utc   end end  t = Time.now                    # => Thu Jan 15 21:26:36 -0500 2009 t.round_off(15.minutes)         # => Thu Jan 15 21:30:00 -0500 2009 t.floor(15.minutes)             # => Thu Jan 15 21:15:00 -0500 2009 

Note: ActiveSupport was only necessary for the pretty 15.minutes argument. If you don't want that dependency, use 15 * 60 instead.

Answer 2

I am not very familiar with the syntax of ruby but you can round down to the nearest 15 minutes using modulo. (i.e. x - (x modulo 15)). I would guess the syntax would be something like

t.min - ( t.min % 15) 

This will make your set of possible values 0, 15, 30, and 45. Assuming 0 <= t.min <= 59.