From: Josh Cheek <josh.cheek@...>
Date: 2009-08-30T16:00:59+09:00
Subject: Re: Sorting an array by multiple elements?

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On Sun, Aug 30, 2009 at 1:30 AM, Paul <tester.paul@gmail.com> wrote:

> Hi there, I have an array of arrays that I want to sort by multiple
> elements.
>
> Sample data in the array looks like: [ [ id, date, num, name ], [ id,
> date, num, name ], ... ]
>
> I need to sort by : (1) name, (2) date, and (3) id.
>
> I can sort by any one element in the array no problem using something
> like :
> > summary_data.sort! { |a,b| a[ 3 ] <=> b[ 3 ] }
>
> Unfortunately, I can't do this line more than once because it blows
> away any previous sorting.
>
> I found a few pages on the internet that describe how to "sort an
> array of Ruby objects by multiple class fields", however, I don't know
> how to create a "class field".  I'm looking at an array, not a class.
>
> Is there a way to do this or do I need to convert my data to something
> else so I can do what I need?
>
> Please help.
>
> Thanks.
>
>

data = [  [ 1 , Time.now , 4, "barny" ] ,
          [ 1 , Time.now , 1, "cliff" ] ,
          [ 2 , Time.now , 3, "alfie" ] ,
          [ 2 , Time.now , 2, "alfie" ] ]

#you can assign the values of the arrays to specific names by grouping
data.sort do |(a_id,a_date,a_num,a_name) , (b_id,b_date,b_num,b_name)|

  first  =   a_id <=> b_id     #first condition
  second =  a_num <=> b_num    #second condition

  first.zero? ? second : first #if they are equal on first
                               #then return second

end.each{ |d| p d }            #inspect each one

__END__

output:
[1, Sun Aug 30 01:55:02 -0500 2009, 1, "cliff"]
[1, Sun Aug 30 01:55:02 -0500 2009, 4, "barny"]
[2, Sun Aug 30 01:55:02 -0500 2009, 2, "alfie"]
[2, Sun Aug 30 01:55:02 -0500 2009, 3, "alfie"]

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