From: Robert Klemme <bob.news@...>
Date: 2005-10-26T20:22:03+09:00
Subject: Re: sort on multiple attributes

Terje Tjervaag wrote:
> Hi,
>
> Just thought I'd write this to the list, since it wasn't immediately
> obvious to me how to do it and I couldn't find it written anywhere on
> the web..
>
> Say you have an array of these music tracks:
> Track = Struct.new("Track", :name, :artist, :album, :track_number)
>
> .and you want to sort the array first by artist, then by album within
> that artist and finally by track number within the album, this can
> still be done by a pretty neat sort block:
>
> sorted_tracks = tracks.sort do |a,b|
>     if a.artist != b.artist
>         a.artist <=> b.artist
>     elsif a.album != b.album
>         a.album <=> b.album
>     else
>         a.track_number.to_i <=> b.track_number.to_i
>     end
> end

Btw, IMHO you should not need track_number.to_i as they should really be
stored as numbers.

Alternative

tracks.sort do |a,b|
  [:artist, :album, :track_number].each do |field|
    c = a.send(field) <=> b.send(field)
    return c unless c == 0
  end
  0
end

<shameless advertising>
I have also a related RCR pending that still can make it into the std
lib...
http://rcrchive.net/rcr/show/293
</shameless advertising>

Kind regards

    robert