Soundex calculation (See related posts)

class Soundex
  ALPHA_MAP = { 'a' => nil, 'b' => '1', 'c' => '2', 'd' => '3', 'e' => nil, 'f' => '1',
                'g' => '2', 'h' => nil, 'i' => nil, 'j' => '2', 'k' => '2', 'l' => '4',
                'm' => '5', 'n' => '5', 'o' => nil, 'p' => '1', 'q' => '2', 'r' => '6',
                's' => '2', 't' => '3', 'u' => nil, 'v' => '1', 'w' => nil, 'x' => '2',
                'y' => nil, 'z' => 2
              }
              
  def self.calculate(aName)
    ary = []
    # map all the letters in the supplied name
    aName.downcase.each_byte{|ltr| ary.push(ALPHA_MAP[ltr.chr])}
    # now drop out repeated values
    ary.length.downto(1){ |idx| ary[idx] = nil if ary[idx]==ary[idx-1] }
    # remove the nil elements
    ary.compact!
    # pad with zeroes
    0.upto(2){ ary.push('0')}
    # Replace the first value with the first letter of the supplied name
    ary[0] = aName[0].chr
    # return the first four elements of the array as a string
    return ary[0..3].to_s
  end
end