midisort.rb

# Put your .mid file in a "midi" directory next to this file.
# Then, in your terminal in the directory that this file is in:
#  gem install midilib
#  ruby ./midisort.rb
# The _sorted MIDI file is now in the "midi" directory.

require 'midilib'

sequence = MIDI::Sequence.new()

# Read the contents of a MIDI file into the sequence.
filename = Dir.glob('./midi/*.mid').first
File.open("#{filename}", 'rb') do |file|
  sequence.read(file)
end

notes = []

sequence.each do |track|
  events = track.events
  events.each_with_index do |event, i| 
    next unless event.is_a?(MIDI::NoteEvent)
    if event.respond_to?(:off)
      notes << {
        note:  event.note,
        note_name: MIDI::Utils.note_to_s(event.note),
        duration: event.off.time_from_start - event.time_from_start
      }
    end
  end
end

# Explore variations by uncommenting a different sorting algorithm. Only one uncommented at a time!

# Randomize
sorted_notes = notes.sort{ |a,b| rand(1) <=> rand(1) }

# Sort by octave-agnostic note names
#sorted_notes = notes.sort{ |a,b| "#{a[:note_name]}" <=> "#{b[:note_name]}" }

# Sort by octave-aware note names
#sorted_notes = notes.sort{ |a,b| "#{a[:note_name]}-#{a[:note]}" <=> "#{b[:note_name]}-#{b[:note]}" }

# Sort by octave-aware note names and durations
#sorted_notes = notes.sort{ |a,b| "#{a[:note_name]}-#{a[:note]}-#{a[:duration]}" <=> "#{b[:note_name]}-#{b[:note]}-#{b[:duration]}" }


sequence.each do |track|
  track.each do |event| 
    next unless event.is_a?(MIDI::NoteEvent)
    if event.respond_to?(:off)
      note = sorted_notes.pop
      event.note = note[:note]
      event.off.note = note[:note]
      event.off.time_from_start = event.off.time_from_start - event.time_from_start
    end
    track.recalc_times
  end
end

output_filename = filename.gsub(".mid", "_sorted.mid")

File.open(output_filename, 'wb') do |file|
  sequence.write(file)
end