From: Paul <tester.paul@...>
Date: 2007-03-20T01:25:07+09:00
Subject: Sorting Dates and Times in an array

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?