Sorting Array Of Dates

chandu4ruby · October 30, 2008, 2:28am

Hi, Everyone I am a newbie to ruby…

just started with some examples

i have array

date = [‘12/09/2007’,‘06/06/2004’,‘10/06/2005’]

i wanted to sort dates in ascending order i.e
[‘06/06/2004’,‘10/06/2005’,‘12/09/2007’]

tried using

p data.sort

could any one explain me whether there is built in class or need to
break tha date string

yyyy mm dd and compare …

regards
chandu

chandu4ruby · October 30, 2008, 2:39am

From: Chandu C. [mailto:[email protected]]

i wanted to sort dates in ascending order i.e

[‘06/06/2004’,‘10/06/2005’,‘12/09/2007’]

could any one explain me whether there is built in class or need to

break tha date string

yyyy mm dd and compare …

you have the idea. just continue reading more on ruby…

eg,

date = [‘12/09/2007’,‘06/06/2004’,‘10/06/2005’]
=> [“12/09/2007”, “06/06/2004”, “10/06/2005”]

date.sort_by{|d| m,d,y=d.split(“/”);[y,m,d]}
=> [“06/06/2004”, “10/06/2005”, “12/09/2007”]

chandu4ruby · October 30, 2008, 2:47am

Works for me in IRB:

date = [‘12/09/2007’,‘06/06/2004’,‘10/06/2005’]
=> [“12/09/2007”, “06/06/2004”, “10/06/2005”]

p date.sort
[“06/06/2004”, “10/06/2005”, “12/09/2007”]
=> nil

If it didn’t work for you, could it be that you assigned to date but
called
sort on data?

Regards,
Craig

chandu4ruby · October 30, 2008, 9:29am

2008/10/30 Chandu C. [email protected]:

Hi, Everyone I am a newbie to ruby…

just started with some examples

i have array

date = [‘12/09/2007’,‘06/06/2004’,‘10/06/2005’]

This is not an array of dates - it’s an array of strings.

i wanted to sort dates in ascending order i.e
[‘06/06/2004’,‘10/06/2005’,‘12/09/2007’]

tried using

p data.sort

could any one explain me whether there is built in class or need to
break tha date string

If these are dates you should use Date.

irb(main):005:0> date = [‘12/09/2007’,‘06/06/2004’,‘10/06/2005’]
=> [“12/09/2007”, “06/06/2004”, “10/06/2005”]
irb(main):006:0> real = date.map {|s| Date.parse s}
=> [#<Date: 4908887/2,0,2299161>, #<Date: 4906325/2,0,2299161>,
#<Date: 4907299/2,0,2299161>]
irb(main):007:0> puts real.sort
2004-06-06
2005-10-06
2007-12-09
=> nil

If for some serious reason you cannot use Date you should at least sort
by Date:

irb(main):009:0> puts date.sort_by {|s| Date.parse s}
06/06/2004
10/06/2005
12/09/2007
=> nil
irb(main):010:0>

You need to require ‘date’ for this to work.

Kind regards

robert

chandu4ruby · October 30, 2008, 10:15am

Chandu C. wrote:

i have array

date = [‘12/09/2007’,‘06/06/2004’,‘10/06/2005’]

i wanted to sort dates in ascending order i.e
[‘06/06/2004’,‘10/06/2005’,‘12/09/2007’]

Apart from the other solutions mentioned, you could also just use ISO
dates instead:

date = [‘2007-09-12’,‘2004-06-06’,‘2005-06-10’]

As well as sorting natively, this also has the advantage of being
absolutely clear which part is the month and which is the day. (In your
example, I can’t tell whether you are using American middle-endian dates
or not)

Regards,

Brian.

chandu4ruby · October 30, 2008, 4:01pm

Josef ‘Jupp’ Schugt wrote:

def datecmp(a, b, reasonable = true)
arra, arrb = a.split(’/’), b.split(’/’)
cmp = (arra[2] <=> arrb[2])
return cmp if (cmp = (arra[2] <=> arrb[2])) != 0
if reasonable
(cmp = (arra[0] <=> arrb[0])) != 0 ? cmp : (arra[1] <=> arrb[1])
else
(cmp = (arra[1] <=> arrb[1])) != 0 ? cmp : (arra[0] <=> arrb[0])
end
end

date = [‘12/01/2007’, ‘11/02/2007’, ‘11/11/2005’]
puts “reasonable date format”
puts date.sort { |a, b| datecmp(a, b) }
puts “\nno reasonable date format”
puts date.sort { |a, b| datecmp(a, b, false) }

I think you got “reasonable” and “unreasonable” reversed (unless you are
American

Here is a shorter solution:

MapR = lambda { |x| x.split(’/’).values_at(2,1,0) }
MapU = lambda { |x| x.split(’/’).values_at(2,0,1) }

date = [‘12/01/2007’, ‘11/02/2007’, ‘11/11/2005’]
puts “reasonable date format”
puts date.sort_by(&MapR)
puts “\nno reasonable date format”
puts date.sort_by(&MapU)

chandu4ruby · October 30, 2008, 6:05pm

On Oct 30, 10:00 am, Brian C. [email protected] wrote:

end
Here is a shorter solution:

MapR = lambda { |x| x.split(‘/’).values_at(2,1,0) }
MapU = lambda { |x| x.split(‘/’).values_at(2,0,1) }

date = [‘12/01/2007’, ‘11/02/2007’, ‘11/11/2005’]
puts “reasonable date format”
puts date.sort_by(&MapR)
puts “\nno reasonable date format”
puts date.sort_by(&MapU)

MAP_R = proc{|x| x.split(‘/’).reverse }
MAP_U = proc{|x| y=x.split(‘/’); [y.pop,y] }

dates = %w(12/01/2007 11/02/2007 11/11/2005)
puts “reasonable date format”
puts dates.sort_by(&MAP_R)
puts “unreasonable date format”
puts dates.sort_by(&MAP_U)

chandu4ruby · October 30, 2008, 7:39pm

On Thu, 30 Oct 2008 16:00:56 +0100, Brian C. [email protected]
wrote:

I think you got “reasonable” and “unreasonable” reversed (unless you are
American

oops, you are right That much on quick hacks… ^^

Josef ‘Jupp’ Schugt

chandu4ruby · October 30, 2008, 1:48pm

On Thu, 30 Oct 2008 02:27:32 +0100, Chandu C. [email protected]
wrote:

Hi, Everyone I am a newbie to ruby…

just started with some examples

i have array

date = [‘12/09/2007’,‘06/06/2004’,‘10/06/2005’]

i wanted to sort dates in ascending order i.e
[‘06/06/2004’,‘10/06/2005’,‘12/09/2007’]

you forgot to mention if the date format is reasonable (dd/mm/yyyy) or
not
(mm/dd/yyyy) - reasonable in the sense that the parts have an ascending
or
descending significance and not an arbitrary one.

Anyway, here’s a solution for both cases:

def datecmp(a, b, reasonable = true)
arra, arrb = a.split(‘/’), b.split(‘/’)
cmp = (arra[2] <=> arrb[2])
return cmp if (cmp = (arra[2] <=> arrb[2])) != 0
if reasonable
(cmp = (arra[0] <=> arrb[0])) != 0 ? cmp : (arra[1] <=> arrb[1])
else
(cmp = (arra[1] <=> arrb[1])) != 0 ? cmp : (arra[0] <=> arrb[0])
end
end

date = [‘12/01/2007’, ‘11/02/2007’, ‘11/11/2005’]
puts “reasonable date format”
puts date.sort { |a, b| datecmp(a, b) }
puts “\nno reasonable date format”
puts date.sort { |a, b| datecmp(a, b, false) }

that results in

reasonable date format
11/11/2005
11/02/2007
12/01/2007

no reasonable date format
11/11/2005
12/01/2007
11/02/2007

but besides that the normal date format is yyyy-mm-dd.

I don’t know about the situation in other countries but in Germany the
date format you SHOULD use (in an RFC sense, the DIN standard says so)
is
that ISO standard form. Other formats are only tolerable but not
desireable. Which does not mean that many Germans use that format. You
hear me frequently protest against forms that still use antiquated date
formats

Josef ‘Jupp’ Schugt