How do I get the number of seconds between two DateTimes in Ruby on Rails

Question

I've got code that does time tracking for employees. It creates a counter to show the employee how long they have been clocked in for.

This is the current code:

  start_time = Time.parse(self.settings.first_clock_in)
  total_seconds = Time.now - start_time
  hours = (total_seconds/ 3600).to_i
  minutes = ((total_seconds % 3600) / 60).to_i
  seconds = ((total_seconds % 3600) % 60).to_i

This works fine. But because Time is limited to the range of 1970 - 2038 we are trying to replace all Time uses with DateTimes. I can't figure out how to get the number of seconds between two DateTimes. Subtracting them yields a Rational which I don't know how to interpret, whereas subtracting Times yields the difference in seconds.

NOTE: Since Ruby 1.9.2, the hard limit of Time is removed. However, Time is optimized for values between 1823-11-12 and 2116-02-20.

score 97 · Accepted Answer · answered Feb 19 '09 at 23:10

97

Subtracting two DateTimes returns the elapsed time in days, so you could just do:

elapsed_seconds = ((end_time - start_time) * 24 * 60 * 60).to_i

answered Feb 19 '09 at 23:10

David Ma

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Ah, I knew it returned it in days, I didn't know that this would include fractions of a day as well. Thanks. – Tilendor Feb 20 '09 at 00:00
4

This doesn't work correctly in case of a Leap second (https://en.wikipedia.org/wiki/Leap_second). – Rok Kralj Mar 17 '13 at 20:35
47

Just a note to anyone else who may be confused by this. Yes, subtracting two `DateTime`s returns elapsed time in days. However, in Rails a model attribute that you migrate as `datetime` may actually be an `ActiveSupport::TimeWithZone`, and subtracting two of those returns elapsed time in *seconds*. – evanrmurphy Oct 07 '13 at 21:49
4

I'm using this and getting a fraction, the datetimes are 2 seconds apart, 15 and 13, but I'm getting 1.939s instead of 2s and .to_i is truncating to 1 second. – ckarbass Oct 29 '13 at 05:14

score 52 · Answer 2 · edited Oct 03 '17 at 15:13

52

Or, more readably:

diff = datetime_1 - datetime_2
diff * 1.days # => difference in seconds; requires Ruby on Rails

Note, what you or some other searchers might really be looking for is this:

diff = datetime_1 - datetime_2
Date.day_fraction_to_time(diff) # => [h, m, s, frac_s]

edited Oct 03 '17 at 15:13

jameshfisher

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answered May 28 '10 at 20:00

Avram Dorfman

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This doesn't seem to be working with me for (created_at and updated_at). My two numbers are `2016-08-07 20:33:54.863568` and `2016-08-07 20:33:54.788684`, but the difference is 6469.9776. Posgres says those fields are 'timestamps without time zone', if that makes a difference. – CHawk Aug 07 '16 at 20:39
1

NoMethodError: undefined method `days' for 1:Fixnum – android.weasel Mar 10 '17 at 15:08
2

note that .days is a rails method and is not available in ruby without it. – sakurashinken Jun 22 '17 at 17:26
1

This should also help => `diff.days.seconds` – Parikshit Singh Oct 25 '21 at 09:30

Luke · Answer 3 · 2009-02-19T23:19:48.030

34

You can convert them to floats with to_f, though this will incur the usual loss of precision associated with floats. If you're just casting to an integer for whole seconds it shouldn't be big enough to be a worry.

The results are in seconds:

>> end_time.to_f - start_time.to_f
=> 7.39954495429993

>> (end_time.to_f - start_time.to_f).to_i
=> 7

Otherwise, you could look at using to_formatted_s on the DateTime object and seeing if you can coax the output into something the Decimal class will accept, or just formatting it as plain Unix time as a string and calling to_i on that.

edited Feb 19 '09 at 23:19

answered Feb 19 '09 at 23:08

Luke

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Thanks Luke, .to_f conversion is great! It works independently of Date class: either it's a DateTime or ActiveSupport::TimeWithZone. – yaru Nov 20 '15 at 07:22
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NoMethodError: undefined method `to_f' for # – jameshfisher Oct 03 '17 at 15:15

score 24 · Answer 4 · answered Jun 21 '16 at 21:57

24

Others incorrectly rely on fractions or helper functions. It's much simpler than that. DateTime itself is integer underneath. Here's the Ruby way:

stop.to_i - start.to_i

Example:

start = Time.now
 => 2016-06-21 14:55:36 -0700
stop = start + 5.seconds
 => 2016-06-21 14:55:41 -0700
stop.to_i - start.to_i
 => 5

answered Jun 21 '16 at 21:57

Amin Ariana

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This only works on `Time` not `DateTime`: `NoMethodError (undefined method to_i for #)` – Christopher Oezbek Sep 13 '21 at 20:03

Som Poddar · Answer 5 · 2014-11-06T01:45:05.317

8

I am using ruby-2.1.4 and for me the following worked

Time.now - Time.new(2014,11,05,17,30,0)

gave me the time difference in seconds

reference: ruby doc

edited Nov 06 '14 at 01:45

answered Nov 06 '14 at 01:39

Som Poddar

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2

OP is referring to "DateTime" Object not a "Time" object. – Brian Sizemore Jan 18 '16 at 21:14

score 2 · Answer 6 · answered Feb 24 '16 at 14:35

2

there's a method made for that:

Time.now.minus_with_coercion(10.seconds.ago)

equals 10.

Source: http://apidock.com/rails/Time/minus_with_coercion

Hope I helped.

answered Feb 24 '16 at 14:35

Francois

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We are talking about DateTime class not Time class. – user1735921 Jun 30 '16 at 05:50

score 1 · Answer 7 · answered Aug 29 '16 at 09:41

Define a Ruby function like this,

def time_diff(start_time, end_time)
  seconds_diff = (start_time - end_time).to_i.abs

  days = seconds_diff / 86400 
  seconds_diff -= days * 86400

  hours = seconds_diff / 3600  
  seconds_diff -= hours * 3600

  minutes = seconds_diff / 60
  seconds_diff -= minutes * 60

  seconds = seconds_diff

  "#{days} Days #{hours} Hrs #{minutes} Min #{seconds} Sec"
 end

And Call this function,

time_diff(Time.now, Time.now-4.days-2.hours-1.minutes-53.seconds)

How do I get the number of seconds between two DateTimes in Ruby on Rails

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