Module: Kotoshu::Algorithms::Soundex

Defined in:
lib/kotoshu/algorithms/soundex.rb

Overview

Soundex phonetic coding.

Soundex is a phonetic algorithm developed by Robert C. Russell and Margaret King Odell in the early 1900s. A word maps to a four-character code (letter + 3 digits); words that sound alike share a code, which is what Suggestions::Strategies::PhoneticStrategy matches on.

Coding rules (the gem's exact semantics — first letter verbatim, H/W never reset the previous code, non-ASCII stripped after upcase, letter-less words code to the empty string):

  • The first letter is kept verbatim and never coded.
  • B/P/F/V code 1, C/S/K/G/J/Q/X/Z code 2, D/T code 3, L codes 4, M/N code 5, R codes 6; vowels and H/W code 0 (skipped). H and W do NOT reset the previous code; every other coded 0 letter does.
  • Adjacent letters sharing a code collapse to one digit.
  • The code is truncated to and zero-padded to exactly 4 chars.

Examples:

Soundex.code("Robert")   # => "R163"
Soundex.code("Rupert")   # => "R163"
Soundex.code("Ashcraft") # => "A261"
Soundex.code("é")        # => "" (no A-Z letters remain)

Class Method Summary collapse

Class Method Details

.code(word) ⇒ String

Calculate the Soundex code for a word.

Parameters:

  • word (String, nil) —

    The word

Returns:

  • (String) —

    The Soundex code (letter + 3 digits), or "" when the word has no A-Z letters



38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
 
# File 'lib/kotoshu/algorithms/soundex.rb', line 38

def code(word)
  return "" if word.nil? || word.empty?

  letters = word.upcase.gsub(/[^A-Z]/, "")
  return "" if letters.empty?

  # Keep first letter. The code is built into one mutable
  # buffer (`<<`) instead of `code += digit`, which allocated
  # a fresh String per encoded letter — the phonetic sweep
  # pays this once per dictionary word.
  code = +letters[0]

  prev_code = encode(code)
  i = 1
  length = letters.length

  while code.length < 4 && i < length
    encoded = encode(letters[i])

    # Add code if different from previous (ignore h and w)
    code << encoded if encoded != "0" && encoded != prev_code

    prev_code = encoded if encoded != "0"
    i += 1
  end

  # Pad with zeros if needed
  code.ljust(4, "0")[0...4]
end

.encode(char) ⇒ String

Soundex encoding table.

Parameters:

  • char (String) —

    The character

Returns:

  • (String) —

    The encoded digit or "0" for no code



72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
 
# File 'lib/kotoshu/algorithms/soundex.rb', line 72

def encode(char)
  case char.upcase
  when "B", "P", "F", "V"
    "1"
  when "C", "S", "K", "G", "J", "Q", "X", "Z"
    "2"
  when "D", "T"
    "3"
  when "L"
    "4"
  when "M", "N"
    "5"
  when "R"
    "6"
  else
    "0"
  end
end