From: Paul Carvalho <tester.paul@...>
Date: 2009-08-31T00:20:11+09:00
Subject: Re: Sorting an array by multiple elements?

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.

On Aug 30, 3:04 am, Stefano Crocco wrote:

> This should do what you want. It first compares the names then, if they're
> equal, it compares the dates. If the dates are also equal it compares the ids.
>
> summary_data.sort! do |a, b|
>  res = a[3] <=> b[3]
>  res = a[1] <=> b[1] if res == 0
>  res = a[0] <=> b[0] if res == 0
>  res
> end
>

This gives me a 98% solution, which is good enough.  There's a small
catch or trick with my data that I can't work around.

Details on the last 2%:

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?

Cheers!