Re: Music Theory (#229)

Evan Hanson wrote all single >'d lines
> On Wed, Mar 3, 2010 at 8:50 AM, Ben Rho <[e-mail]> wrote:
>> picked up)
> I'm not sure when "susb" would cause an issue -- do you mean an
> instance like Gsusb? I don't know that that's a chord, but the G would
> be read and the susb would raise an exception as an invalid chord
> symbol.
Yes, I do mean like Gsusb. Susb wasn't a valid example, but if it was 
actually the name of a type of chord, it would be counted as Gbsusb. 
Your code (with my comments):
    note[1..-1].scan(/./).each do |n|                        #for every 
character in the input except the first store it in n and do the 
following ( btw an easier way is simply note[1..-1].each('') ):
      if    n == 'b' then flat!                              #if n is b 
then flat the base note
      elsif n == '#' then sharp!                             #else, if n 
is # then sharp the base note
      else  raise ArgumentError, 'Invalid note name!' end    #otherwise 
rase an error
    end                                                      #endfor
For Gbsusb (assuming susb is a valid chord type) get the second 
character, which is b, and if it is b (which it is), flat the base note. 
Then do the same for s, then u, then s, then b (and flat it again), etc. 
On second thought, the sus should hit the ArgumentError, hm.. Can anyone 
explain that?

>> Chord#to_s:
>> �Returns @name
>> But that would only return the input in a fancy way! I don't see how it
>> returns chords.
> 
> It actually returns the individual notes in the chord, as generated by
> Chord#names.
#...#
@name = note[0,1]                   #if note="Hello World" this sets 
@name to 'H'
#...#
#apply sharps and flats to @name
#...#
  def to_s
    @name
  end
#...#
To me it seems that the base note is stored in @name, which is what is 
returned in to_s - so it would just return the base note.

> As an aside, can anyone tell me if there is a slick Ruby way to do
> what is done in cases like my Key#names, Chord#names, Chord#to_s, etc.
> functions, where you're just mapping things from one array to another,
> or from one array to a string, etc?
See Jesús' answer. One thing to add - array * str is the same as 
array.join(str):
[1,2,3]*          #=> ERROR
[1,2,3]*''        #=> '123'
[1,2,3]*' '       #=> '1 2 3'
[1,2,3].join      #=> '123'
[1,2,3].join(' ') #=> '1 2 3'

Wait, I just realized some of my arguments are invalid! For some reason 
I've been looking at the Note class all along, instead of the Chord 
class! *facepalm* Sorry about that..

--------------------------

I started re-doing this Quiz from scratch about an hour ago without 
looking at anyone else's code, unfortunately, the results look about the 
same as David Springer's code (mine follows).

>   # Sharps the note in place... Comments are fun!
I agree! They're also useful for anyone trying to read or debug your 
code! :)

#I'll be making this library bigger, given enough time. I'd copy David 
Springer's (he has given me his permission), but this is case 
insensitive and doesn't have optional notes).
chord_library={
  '7'    => [3,4,3],
  'major'    => [4,3],
  'maj'    => [4,3],
  'major7'  => [4,3,4],
  'maj7'    => [4,3,4],
  'minor'    => [3,4],
  'min'    => [3,4],
  'minor7'  => [3,4,3],
  'min7'    => [3,4,3],
  'm7'    => [3,4,3],
  'sus'    => [7],
  'sus2'    => [2,5],
  'sus4'    => [5,2]
}
rotated_notes = []
while !((chord=gets.to_s.chomp.downcase).empty?)
  base_note = chord[/^[abdeg]b/]
  if (base_note == nil)
    base_note = chord[/^[acdfg]#/]
    if (base_note == nil)
      base_note = chord[/^[a-g]/]
      if (base_note == nil)
        puts 'ERROR: Invalid base note'
        next
      end
    end
  end
  note_list = ((base_note[1,1]=='b') ? (%w(ab a bb b c db d eb e f gb 
g)) : (%w(a a# b c c# d d# e f f# g g#)))
  i=-1
  rotated_notes = note_list.map do
    i += 1
    note_list[(i + note_list.index(base_note))%12]
  end
  variation = ($'.empty?) ? ('major') : ($')
  if (chord_library[variation] == nil)
    puts 'ERROR: Chord not found'
    next
  end
  out = 'The notes in the chord ' + chord.capitalize + ' are: ' + 
base_note.capitalize
  note_tally = 0
  chord_library[variation].each do |note|
    if (note<0)
      next
    end
    out << ' ' + rotated_notes[((note+note_tally)%12)].capitalize
    note_tally += note
  end
  puts out
end
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