Listing missing months in an array of dates - ruby

Question

I have a list of transactions in an array.
=> [Wed, 23 Oct 2013, Mon, 18 Nov 2013, Fri, 22 Nov 2013, Mon, 13 Jan 2014, Tue, 28 Jan 2014, Mon, 03 Feb 2014, Mon, 10 Feb 2014, Tue, 18 Feb 2014, Fri, 07 Mar 2014, Mon, 31 Mar 2014, Mon, 07 Apr 2014, Tue, 10 Jun 2014, Mon, 30 Jun 2014, Mon, 22 Sep 2014, Mon, 06 Oct 2014, Fri, 14 Nov 2014, Tue, 18 Nov 2014, Fri, 26 Dec 2014, Thu, 15 Jan 2015, Mon, 23 Mar 2015, Mon, 20 Apr 2015]
I need to compare the dates of each transaction and list any months that are missing in the list of months and year. Here is what I have now...
#find_transactions = (#user.transactions.find_all { |t| (t.name 'name' })
#trans_dates = #find_transactions.map(&:date).sort!.map { |s| Date.strptime(s, '%Y-%m') }.each_cons(2).map{ |d1,d2| d1.next_month == d2 }
This method currently gives me a true or false if each month is there but I need to actually have the method print a list of months that are missing. I would like to have it print the month and year together.
Here is the response this method gives me...
=> [true, false, true, false, false, true, false, true, false, false, false, true, true]
I want a response like this...
=> [March 2015, December 2014, September 2014]
Thanks in advance!

Answer 1

Edit: For array already being composed of date objects you can do:
require 'date'
dates = [Wed, 23 Oct 2013, Mon, 18 Nov 2013, Fri, 22 Nov 2013, Mon, 13 Jan 2014, Tue, 28 Jan 2014, Mon, 03 Feb 2014, Mon, 10 Feb 2014, Tue, 18 Feb 2014, Fri, 07 Mar 2014, Mon, 31 Mar 2014, Mon, 07 Apr 2014, Tue, 10 Jun 2014, Mon, 30 Jun 2014, Mon, 22 Sep 2014, Mon, 06 Oct 2014, Fri, 14 Nov 2014, Tue, 18 Nov 2014, Fri, 26 Dec 2014, Thu, 15 Jan 2015, Mon, 23 Mar 2015, Mon, 20 Apr 2015]
all_dates = []
dates.first.upto(dates.last) {|x| all_dates << x.strftime('%b %Y') if x.day == 1 || x == dates.first}
d = dates.map {|x| x.strftime('%b %Y')}.uniq
p (all_dates - d)
#=> ["Dec 2013", "May 2014", "Jul 2014", "Aug 2014", "Feb 2015"]
Edit: Below methods are for an array of date strings
You can try this:
require 'date'
dates = ["Wed, 23 Oct 2013", "Mon, 18 Nov 2013", "Fri, 22 Nov 2013", "Mon, 13 Jan 2014", "Tue, 28 Jan 2014", "Mon, 03 Feb 2014", "Mon, 10 Feb 2014", "Tue, 18 Feb 2014", "Fri, 07 Mar 2014", "Mon, 31 Mar 2014", "Mon, 07 Apr 2014", "Tue, 10 Jun 2014", "Mon, 30 Jun 2014", "Mon, 22 Sep 2014", "Mon, 06 Oct 2014", "Fri, 14 Nov 2014", "Tue, 18 Nov 2014", "Fri, 26 Dec 2014", "Thu, 15 Jan 2015", "Mon, 23 Mar 2015", "Mon, 20 Apr 2015"]
all_dates = []
d = dates.map {|x| Date.parse(x[8..-1])}.uniq
counter = d.first
until counter == d.last
all_dates << counter
counter = counter.next_month
end
p (all_dates - d).map {|x| x.strftime('%b %Y')}
#=> ["Dec 2013", "May 2014", "Jul 2014", "Aug 2014", "Feb 2015"]
Another (more concise) way would be:
require 'date'
dates = ["Wed, 23 Oct 2013", "Mon, 18 Nov 2013", "Fri, 22 Nov 2013", "Mon, 13 Jan 2014", "Tue, 28 Jan 2014", "Mon, 03 Feb 2014", "Mon, 10 Feb 2014", "Tue, 18 Feb 2014", "Fri, 07 Mar 2014", "Mon, 31 Mar 2014", "Mon, 07 Apr 2014", "Tue, 10 Jun 2014", "Mon, 30 Jun 2014", "Mon, 22 Sep 2014", "Mon, 06 Oct 2014", "Fri, 14 Nov 2014", "Tue, 18 Nov 2014", "Fri, 26 Dec 2014", "Thu, 15 Jan 2015", "Mon, 23 Mar 2015", "Mon, 20 Apr 2015"]
all_dates = []
d = dates.map {|x| Date.parse(x[8..-1])}.uniq
d.first.upto(d.last) {|x| all_dates << x if x.day == 1}
p (all_dates - d).map {|x| x.strftime('%b %Y')}
#=> ["Dec 2013", "May 2014", "Jul 2014", "Aug 2014", "Feb 2015"]

Answer 2

This is one way you could do that.
Code
require 'date'
def missing_months(dates)
a = dates.map { |s| d = Date.strptime(s, '%a, %d %b %Y'); d - d.day + 1 }
(all_months_in_range(*a.minmax) -a).map { |d| d.strftime('%b %Y') }
end
def all_months_in_range(f,l)
(12*(l.year-f.year)+l.month-f.month+1).times.map do |i|
y,m = (f.month+i).divmod(12)
y += f.year
(m=12; y-=1) if m ==0
Date.new(y,m)
end
end
Example
dates = ['Wed, 23 Oct 2013', 'Mon, 18 Nov 2013', 'Fri, 22 Nov 2013',
'Fri, 14 Nov 2014', 'Tue, 18 Nov 2014', 'Fri, 26 Dec 2014',
'Mon, 13 Jan 2014', 'Tue, 28 Jan 2014', 'Mon, 03 Feb 2014',
'Mon, 31 Mar 2014', 'Mon, 07 Apr 2014', 'Tue, 10 Jun 2014',
'Mon, 30 Jun 2014', 'Mon, 22 Sep 2014', 'Mon, 06 Oct 2014',
'Mon, 10 Feb 2014', 'Tue, 18 Feb 2014', 'Fri, 07 Mar 2014',
'Thu, 15 Jan 2015', 'Mon, 23 Mar 2015', 'Mon, 20 Apr 2015']
missing_months(dates)
#=> ["Dec 2013", "May 2014", "Jul 2014", "Aug 2014", "Feb 2015"]
Notice that the dates needn't be sorted.
Explanation
For the example above:
a = dates.map { |s| d = Date.strptime(s, '%a, %d %b %Y'); d - d.day + 1 }
#=> [#<Date: 2013-10-01 ((2456567j,0s,0n),+0s,2299161j)>,
# #<Date: 2013-11-01 ((2456598j,0s,0n),+0s,2299161j)>,
# ...
# #<Date: 2015-04-01 ((2457114j,0s,0n),+0s,2299161j)>]
Notice that each of these dates is on the first of the month. Next, obtain the first and last of these dates:
f,l = a.minmax
f #=> [#<Date: 2013-10-01 ((2456567j,0s,0n),+0s,2299161j)>,
l #=> #<Date: 2015-04-01 ((2457114j,0s,0n),+0s,2299161j)>]
Now pass f and l to all_months_in_range to create an array that contains a date object for the first day of each month between f and l.
b = all_months_in_range(f,l)
#=> [#<Date: 2013-10-01 ((2456567j,0s,0n),+0s,2299161j)>,
# #<Date: 2013-11-01 ((2456598j,0s,0n),+0s,2299161j)>,
# ...
# #<Date: 2015-04-01 ((2457114j,0s,0n),+0s,2299161j)>]
b.size #=> 19
I will skip an explanation of this helper method, as it is quite straightforward.
Compute that difference between arrays b and a to obtain the missing beginning-of-month dates:
c = b-a
#=> [#<Date: 2013-12-01 ((2456628j,0s,0n),+0s,2299161j)>,
# #<Date: 2014-05-01 ((2456779j,0s,0n),+0s,2299161j)>,
# #<Date: 2014-07-01 ((2456840j,0s,0n),+0s,2299161j)>,
# #<Date: 2014-08-01 ((2456871j,0s,0n),+0s,2299161j)>,
# #<Date: 2015-02-01 ((2457055j,0s,0n),+0s,2299161j)>]
Lastly, convert these dates to the desired format:
c.map { |d| d.strftime('%b %Y') }
#=> ["Dec 2013", "May 2014", "Jul 2014", "Aug 2014", "Feb 2015"]
Addendum: after reading #Sid's answer, I see I could have saved myself some trouble in my helper method by using Date#next_month:
def all_months_in_range(f,l)
(12*(l.year-f.year)+l.month-f.month+1).times.map { |i| f.next_month(i) }
end

Answer 3

This isn't very elegant, but it worked. I started with your original code, #SupremeA, and built off of that.
require 'date'
dates = ['Wed, 23 Oct 2013', 'Mon, 18 Nov 2013', 'Fri, 22 Nov 2013', 'Mon, 13 Jan 2014', 'Tue, 28 Jan 2014', 'Mon, 03 Feb 2014', 'Mon, 10 Feb 2014', 'Tue, 18 Feb 2014', 'Fri, 07 Mar 2014', 'Mon, 31 Mar 2014', 'Mon, 07 Apr 2014', 'Tue, 10 Jun 2014', 'Mon, 30 Jun 2014', 'Mon, 22 Sep 2014', 'Mon, 06 Oct 2014', 'Fri, 14 Nov 2014', 'Tue, 18 Nov 2014', 'Fri, 26 Dec 2014', 'Thu, 15 Jan 2015', 'Mon, 23 Mar 2015', 'Mon, 20 Apr 2015']
new_dates = []
dates.each { |d| new_dates.push(Date.parse(d).strftime('%B %Y')) }
sorted_dates = new_dates.map { |s| Date.strptime(s, '%B %Y') }.sort.uniq
missing_months = []
sorted_dates.each_cons(2) do |d1,d2|
d = d1
while d.next_month != d2
missing_months.push(d.next_month.strftime('%B %Y'))
d = d >> 1
end
end
p missing_months
=> ["December 2013", "May 2014", "July 2014", "August 2014", "February 2015"]