How can I find the number of days between two Date objects in Ruby?

How can I find the number of days between two Date objects?

10 Answers

Subtract the beginning date from the end date:

endDate - beginDate 

6

irb(main):005:0> a = Date.parse("12/1/2010")
=> #<Date: 4911063/2,0,2299161>
irb(main):007:0> b = Date.parse("12/21/2010")
=> #<Date: 4911103/2,0,2299161>
irb(main):016:0> c = b.mjd - a.mjd
=> 20

This uses a Modified Julian Day Number.

From wikipedia:

The Julian date (JD) is the interval of time in days and fractions of a day since January 1, 4713 BC Greenwich noon, Julian proleptic calendar.

This may have changed in Ruby 2.0

When I do this I get a fraction. For example on the console (either irb or rails c)

2.0.0-p195 :005 > require 'date' => true
2.0.0-p195 :006 > a_date = Date.parse("25/12/2013") => #<Date: 2013-12-25 ((2456652j,0s,0n),+0s,2299161j)>
2.0.0-p195 :007 > b_date = Date.parse("10/12/2013") => #<Date: 2013-12-10 ((2456637j,0s,0n),+0s,2299161j)>
2.0.0-p195 :008 > a_date-b_date => (15/1) 

Of course, casting to an int give the expected result

2.0.0-p195 :009 > (a_date-b_date).to_i => 15 

This also works for DateTime objects, but you have to take into consideration seconds, such as this example

2.0.0-p195 :017 > a_date_time = DateTime.now => #<DateTime: 2013-12-31T12:23:03-08:00 ((2456658j,73383s,725757000n),-28800s,2299161j)>
2.0.0-p195 :018 > b_date_time = DateTime.now-20 => #<DateTime: 2013-12-11T12:23:06-08:00 ((2456638j,73386s,69998000n),-28800s,2299161j)>
2.0.0-p195 :019 > a_date_time - b_date_time => (1727997655759/86400000000)
2.0.0-p195 :020 > (a_date_time - b_date_time).to_i => 19
2.0.0-p195 :021 > c_date_time = a_date_time-20 => #<DateTime: 2013-12-11T12:23:03-08:00 ((2456638j,73383s,725757000n),-28800s,2299161j)>
2.0.0-p195 :022 > a_date_time - c_date_time => (20/1)
2.0.0-p195 :023 > (a_date_time - c_date_time).to_i => 20 

In Ruby 2.1.3 things have changed:

> endDate = Date.new(2014, 1, 2) => #<Date: 2014-01-02 ((2456660j,0s,0n),+0s,2299161j)>
> beginDate = Date.new(2014, 1, 1) => #<Date: 2014-01-01 ((2456659j,0s,0n),+0s,2299161j)>
> days = endDate - beginDate => (1/1)
> days.class => Rational
> days.to_i => 1 

How about this?

(beginDate...endDate).count

The Range is a set of unique serials. And ... is an exclusive Range literal.

So beginDate..(endDate - 1) is same. Except is not.

In case when beginDate equals endDate, first element will be excluded because of uniqueness and ... will exclude last one. So if we want to .count dates between today and today it will return 0.

1

This worked for me:

(endDate - beginDate).to_i

all of these steered me to the correct result, but I wound up doing

DateTime.now.mjd - DateTime.parse("01-01-1995").mjd

3

Try this:

num_days = later_date - earlier_date

days = (endDate - beginDate)/(60*60*24)

1

Well, take care of what you mean by "between" too...

days_apart = (to - from).to_i # from + days_apart = to
total_days = (to - from).to_i + 1 # number of "selected" days
in_between_days = (to - from).to_i - 1 # how many days are in between from and to, i.e. excluding those two days

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