Le lundi 19 mars 2007 17:25, Paul a ñÄrit
> Hi there.  I am having a bit of trouble trying to solve a particular
> sorting problem with an array of data.
>
> Please bear with me for a moment regarding the setup of this problem.
> I don't currently have any control over the input data.  I am just
> trying to format the report of this data as per the requirement.
>
> I have the following sample array data to work with:
> @date_array = [['2/22/07','1:03 pm'],['3/9/07','10:45 pm'],
> ['3/1/07','1:52 pm'],['3/13/07','2:00 pm'],['2/28/07','10:45 am'],
> ['3/5/07','4:00 pm'],['2/14/07','5:00 pm'],['3/9/07','10:18 am'],
> ['3/13/07','11:15 am']]
>
> (The actual array contains more data, but this is good enough to work
> on this problem.  BTW, date format = mm/dd/yy.)
>
> Requirement:
> 1) Sort in descending order by Date (i.e. @date_array[x][0] )
> 2) Sort in ascending order by Time (i.e. @date_array[x][1] )
>
> Elsewhere in the script, I use the following line to sort by a
>
> particular element in a row:
> > @fields.sort! { |a,b| b[ x ] <=> a[ x ] }     # i.e. descending sort
>
> This works quite nicely for string and numeric fields, but *not* for
> Date or Time string fields.  As an example, when I try it with the
> above data I get the following:
> ----
> puts 'Descending Sort - By Date:'
> @date_array.sort! { |a,b| b[ 0 ] <=> a[ 0 ] }
> @date_array.each_index do |row|
> 	puts "row # #{row} = " + @date_array[row].join(" : ")
> end
> ----
> Descending Sort - By Date:
> row # 0 = 3/9/07 : 10:18 am
> row # 1 = 3/9/07 : 10:45 pm
> row # 2 = 3/5/07 : 4:00 pm
> row # 3 = 3/13/07 : 2:00 pm
> row # 4 = 3/13/07 : 11:15 am
> row # 5 = 3/1/07 : 1:52 pm
> row # 6 = 2/28/07 : 10:45 am
> row # 7 = 2/22/07 : 1:03 pm
> row # 8 = 2/14/07 : 5:00 pm
> ----
>
> --> Which is a nice string sort again, but not a date sort.
>
> I know I'll have to write a method to deal with these two columns of
> data, but I'm not sure where to start.  I've tried googling solutions
> in both this discussion group and the internet but so far haven't
> turned up anything I can use.
>
> Suggestions?


Hi Paul,

You may want to first convert your dates/times to real Time objects, so that 
they can be compared.

Here is my solution :

require 'pp'
pp @date_array.sort_by {|ary| ary.map{|elt| Time.parse(elt) } }
[["2/14/07", "5:00 pm"],
 ["2/22/07", "1:03 pm"],
 ["2/28/07", "10:45 am"],
 ["3/1/07", "1:52 pm"],
 ["3/5/07", "4:00 pm"],
 ["3/9/07", "10:18 am"],
 ["3/9/07", "10:45 pm"],
 ["3/13/07", "11:15 am"],
 ["3/13/07", "2:00 pm"]]
=> nil

A quick explanation :
@date_array is sorted with sort_by, because we want to sort the array 
according to a simple criteria. For the comparison, each element of the array 
(ie the date and the time string) is converted to a Time object with 
Time#parse, and is kept in an array (this is why I used #map).

Doing so, the original arrays of Strings will be sorted, according to the 
order of the Arrays containing the real Time objects. For example on a single 
element of your original array :
["2/14/07", "5:00 pm"].map{|el| Time.parse(el)}
=> [Wed Feb 14 00:00:00 +0100 2007, Mon Mar 19 17:00:00 +0100 2007]


Instead of comparing arrays that contains one element for the date and another 
element for the time, we could have created only one Time object representing 
both :

@date_array.sort_by {|ary| Time.parse("#{ary.first} #{ary.last}") }

Regards.

-- 
Olivier Renaud