Musical Script Solution - arrays

Question

guys
I am a beginner in ruby ​​and in my practices I thought of a musical script and there is a point that is making me sleepy: The moment I type Scale.major_by_note ('C') in irb everything is fine, but if I type Scale.major_by_note ('C #'), it doesn't work, for it to work I must put a "C # / Db", help me to make sure with both "C" and "C #" and "C # / Db", thank you! below is the script:
class Scale
NATURAL = %w[C D E F G A B].freeze
ACCIDENT = %w[C# Db D# Eb F# Gb G# Ab A# Bb].freeze
CHROMATIC = %w[C C#/Db D D#/Eb E F F#/Gb G G# A A#/Bb B].freeze
SCALE_MAJOR_PATTERN = [0, 2, 4, 5, 7, 9, 11, 12].freeze # T T st T T T st
SCALE_MINOR_PATTERN = [0, 2, 3, 5, 7, 8, 10, 12].freeze # T st T T st T T
def self.show_all_scales(note)
major = Scale.major_by_note(note)
minor = Scale.minor_by_note(note)
all = { major: major, minor: minor}
end
def self.major_by_note(note)
major_note_index = CHROMATIC.index(note)
SCALE_MAJOR_PATTERN.map do |major_interval| # Interação
major_scale_note_index = major_note_index + major_interval
if major_scale_note_index <= (CHROMATIC.length - 1)
CHROMATIC[major_scale_note_index]
else
reseted_major_scale_note_index = major_scale_note_index - CHROMATIC.length
CHROMATIC[reseted_major_scale_note_index]
end
end
end
def self.minor_by_note(note)
minor_note_index = CHROMATIC.index(note)
SCALE_MINOR_PATTERN.map do |minor_interval|
minor_scale_note_index = minor_note_index + minor_interval
if minor_scale_note_index <= (CHROMATIC.length - 1)
CHROMATIC[minor_scale_note_index]
else
reseted_minor_scale_note_index = minor_scale_note_index - CHROMATIC.length
CHROMATIC[reseted_minor_scale_note_index]
end
end
end
end```

Answer 1

When you type
%w[C C#/Db D D#/Eb E F F#/Gb G G# A A#/Bb B]
Ruby is turning this into an Array of Strings:
["C", "C#/Db", "D", "D#/Eb", "E", "F", "F#/Gb", "G", "G#", "A", "A#/Bb", "B"]
Now while you know C# and Db are the same note, Ruby doesn't. It thinks the note in this case is called C#/Db. When it tries to find CHROMATIC.index("C#") it is returning nil because there is no C# in the Array.
A solution could be to write it like this:
CHROMATIC = %w[C C# D D# E F F# G G# A A# B].freeze
CHROMATIC_PAIR_MAP = {
"Db" => "C#",
"Eb" => "D#",
"Gb" => "F#",
"Ab" => "B#",
}
...
def self.index_of_note(note)
CHROMATIC.index(note) ||
CHROMATIC.index(CHROMATIC_PAIR_MAP[note])
end
def self.major_by_note(note)
major_note_index = index_of_note(note)
Here I am making a new helper method to get the index of the note by either getting it straight from CHROMATIC array, or looking up a the note key in the CHROMATIC_PAR_MAP Hash. It will only perform the lookup in the Hash if CHROMATIC.index(note) returns nil.
This is what I get in the console (irb):
irb(main):191:0> Scale.major_by_note("C#")
=> ["C#", "D#", "F", "F#", "G#", "A#", "C", "C#"]
irb(main):192:0> Scale.major_by_note("Db")
=> ["C#", "D#", "F", "F#", "G#", "A#", "C", "C#"]
irb(main):193:0> Scale.major_by_note("D#")=> ["D#", "F", "G", "G#", "A#", "C", "D", "D#"]
irb(main):194:0> Scale.major_by_note("Eb")=> ["D#", "F", "G", "G#", "A#", "C", "D", "D#"]
The full new class:
class Scale
NATURAL = %w[C D E F G A B].freeze
ACCIDENT = %w[C# Db D# Eb F# Gb G# Ab A# Bb].freeze
CHROMATIC = %w[C C# D D# E F F# G G# A A# B].freeze
SCALE_MAJOR_PATTERN = [0, 2, 4, 5, 7, 9, 11, 12].freeze # T T st T T T st
SCALE_MINOR_PATTERN = [0, 2, 3, 5, 7, 8, 10, 12].freeze # T st T T st T T
CHROMATIC_PAIR_MAP = {
"Db" => "C#",
"Eb" => "D#",
"Gb" => "F#",
"Ab" => "B#",
}
def self.show_all_scales(note)
major = Scale.major_by_note(note)
minor = Scale.minor_by_note(note)
all = { major: major, minor: minor}
end
def self.major_by_note(note)
major_note_index = index_of_note(note)
SCALE_MAJOR_PATTERN.map do |major_interval| # Interação
major_scale_note_index = major_note_index + major_interval
if major_scale_note_index <= (CHROMATIC.length - 1)
CHROMATIC[major_scale_note_index]
else
reseted_major_scale_note_index = major_scale_note_index - CHROMATIC.length
CHROMATIC[reseted_major_scale_note_index]
end
end
end
def self.minor_by_note(note)
minor_note_index = CHROMATIC.index(note)
SCALE_MINOR_PATTERN.map do |minor_interval|
minor_scale_note_index = minor_note_index + minor_interval
if minor_scale_note_index <= (CHROMATIC.length - 1)
CHROMATIC[minor_scale_note_index]
else
reseted_minor_scale_note_index = minor_scale_note_index - CHROMATIC.length
CHROMATIC[reseted_minor_scale_note_index]
end
end
end
def self.index_of_note(note)
CHROMATIC.index(note) ||
CHROMATIC.index(CHROMATIC_PAIR_MAP[note])
end
end