From: "David A. Black" <dblack@...>
Date: 2009-08-31T00:41:17+09:00
Subject: Re: Sorting an array by multiple elements?

Hi --

On Mon, 31 Aug 2009, Paul Carvalho wrote:

> Thanks for the great feedback!  I couldn't find good documentation for
> the 'sort_by' and the examples provided didn't work with my data.  It
> did nothing actually, which surprised me.  Josh and Stefano's approach
> worked well enough.

The nothing result seems strange. This:

   data = [ [3, "2009-08-23", 3, "alfie"],
            [5, "2009-08-24", 1, "cliff"],
            [6, "2009-08-23", 3, "alfie"],
            [1, "2009-08-21", 4, "barny"],
            [2, "2009-08-21", 2, "alfie"] ]
   data.sort_by {|id, date, num, name| [name, date, id] }

gives me:

     [ [2, "2009-08-21", 2, "alfie"],
       [3, "2009-08-23", 3, "alfie"],
       [6, "2009-08-23", 3, "alfie"],
       [1, "2009-08-21", 4, "barny"],
       [5, "2009-08-24", 1, "cliff"]]

For documentation: ri Enumerable#sort_by

> Unfortunately, the data in the array is not a fixed size.  Sometimes
> it is [ id, date, num, name ] and sometimes it may be [ id, date, num,
> name1, name2 ] (or more names.. I don't know how many since the data
> collection script figures it out as it goes along).
>
> When I do the sort by 'name' (e.g. first = a_name <=> b_name ), all
> the records with _additional_ names appears at the bottom of the list
> as if it were a different name (unexpected).
>
> For example, the output (now) looks like:
>
> [2, "2009-08-21", 2, "alfie"]
> [3, "2009-08-23", 3, "alfie"]
> [6, "2009-08-23", 3, "alfie"]
> [1, "2009-08-21", 4, "barny"]
> [5, "2009-08-24", 1, "cliff"]
> [4, "2009-08-21", 1, "cliff", "bob"]
>
> .. but I expect/want the output to look like:
> [2, "2009-08-21", 2, "alfie"]
> [3, "2009-08-23", 3, "alfie"]
> [6, "2009-08-23", 3, "alfie"]
> [1, "2009-08-21", 4, "barny"]
> [4, "2009-08-21", 1, "cliff", "bob"]
> [5, "2009-08-24", 1, "cliff"]
>
>
> Any thoughts?

Yeah -- sort_by :-)

  data = [ [2, "2009-08-21", 2, "alfie"],
           [6, "2009-08-23", 3, "alfie"],
           [1, "2009-08-21", 4, "barny"],
           [3, "2009-08-23", 3, "alfie"],
           [5, "2009-08-24", 1, "cliff"],
           [4, "2009-08-21", 1, "cliff", "bob"] ]

   data.sort_by {|id, date, num, name| [name, date, id] }

gives me:

        [2, "2009-08-21", 2, "alfie"]
        [3, "2009-08-23", 3, "alfie"]
        [6, "2009-08-23", 3, "alfie"]
        [1, "2009-08-21", 4, "barny"]
        [4, "2009-08-21", 1, "cliff", "bob"]
        [5, "2009-08-24", 1, "cliff"]


David

-- 
David A. Black / Ruby Power and Light, LLC / http://www.rubypal.com
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