sort on multiple attributes

[Terje Tjervaag]

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 =3D 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 =3D tracks.sort do |a,b|
if a.artist !=3D b.artist
a.artist <=3D> b.artist
elsif a.album !=3D b.album
a.album <=3D> b.album
else
a.track_number.to_i <=3D> b.track_number.to_i
end
end

 

[Brian Schröder]

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 =3D 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 =3D tracks.sort do |a,b|
if a.artist !=3D b.artist
a.artist <=3D> b.artist
elsif a.album !=3D b.album
a.album <=3D> b.album
else
a.track_number.to_i <=3D> b.track_number.to_i
end
end

Or you can say
sorted_tracks =3D tracks.sort_by { | track |
[track.artist, track.album, track.track_number]
}

or even:

class Array
def sort_by_att(*attributes)
attributes =3D attributes.flatten
self.sort_by { | e | attributes.map { | a | e.send(a) } }
end
end

sorted_tracks =3D tracks.sort_by_attartist, :album, :track_number)

(warning, untested code, beware of the bug)

regards,

Brian

 

[Martin DeMello]

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:

tracklist.sort_by {|i| [i.artist, i.album, i.track_number] }

works because ruby already defines Array#<=> to check the first entry,
break ties on the second entry, etc.

martin

 

[Terje Tjervaag]

Or you can say
sorted_tracks =3D tracks.sort_by { | track |
[track.artist, track.album, track.track_number]
}

nice! thanks. I had a feeling it could be improved.

 

[Terje Tjervaag]

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Content-Transfer-Encoding: quoted-printable
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Btw, IMHO you should not need track_number.to_i as they should really be
stored as numbers.

I agree - in this case I was playing around with making the most
minimal iTunes Music Library parser I could, hence my use of .to_i.
The current 14 line program is attached, if anyone is curious. It
could be 9 if it wasn't for the error checking.

Alternative

tracks.sort do |a,b|
[:artist, :album, :track_number].each do |field|
c =3D a.send(field) <=3D> b.send(field)
return c unless c =3D=3D 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>

I could see those additions being useful - it is a case of where to
hide the inevitable complexity I suppose, and I think your RCR deals
with it in a way that's very easy to read in the end.

--
Terje

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Content-Type: application/octet-stream; name=itunes.rb
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="itunes.rb"

require 'rexml/document'
if !ARGV[0] then puts "Give me the path to the iTunes Music Library.xml file"; exit end
Track = Struct.new("Track", :artist, :album, :track_number, :name, :location, :genre, :track_count)
tracks = []
begin
REXML:ocument.new(File.new(ARGV[0])).elements.each("plist/dict/dict/dict") do |e|
t = Track.new
e.elements.each("key"){|e|m=e.text.downcase.gsub(" ","_")+"=";t.send(m,e.next_sibling.text) if t.respond_to?(m)}
tracks << t
end
rescue REXML:arseException
puts "iTunes Library file format not recognised"
end
tracks.sort_by{|t|[t.artist,t.album,t.track_number.to_i]}.each{|track| puts track.values[0, 4].join(" - ")}



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