Module: Text::PorterStemming

Defined in:
lib/text/porter_stemming.rb

Overview

:nodoc:

Constant Summary collapse

STEP_2_LIST = 
{
  'ational' => 'ate', 'tional' => 'tion', 'enci' => 'ence', 'anci' => 'ance',
  'izer' => 'ize', 'bli' => 'ble',
  'alli' => 'al', 'entli' => 'ent', 'eli' => 'e', 'ousli' => 'ous',
  'ization' => 'ize', 'ation' => 'ate',
  'ator' => 'ate', 'alism' => 'al', 'iveness' => 'ive', 'fulness' => 'ful',
  'ousness' => 'ous', 'aliti' => 'al',
  'iviti' => 'ive', 'biliti' => 'ble', 'logi' => 'log'
}
STEP_3_LIST = 
{
  'icate' => 'ic', 'ative' => '', 'alize' => 'al', 'iciti' => 'ic',
  'ical' => 'ic', 'ful' => '', 'ness' => ''
}
SUFFIX_1_REGEXP = 
/(
ational  |
tional   |
enci     |
anci     |
izer     |
bli      |
alli     |
entli    |
eli      |
ousli    |
ization  |
ation    |
ator     |
alism    |
iveness  |
fulness  |
ousness  |
aliti    |
iviti    |
biliti   |
logi)$/x
SUFFIX_2_REGEXP = 
/(
al       |
ance     |
ence     |
er       |
ic       |
able     |
ible     |
ant      |
ement    |
ment     |
ent      |
ou       |
ism      |
ate      |
iti      |
ous      |
ive      |
ize)$/x
C =

consonant

"[^aeiou]"
V =

vowel

"[aeiouy]"
CC =

consonant sequence

"#{C}(?>[^aeiouy]*)"
VV =

vowel sequence

"#{V}(?>[aeiou]*)"
MGR0 =

[cc]vvcc… is m>0

/^(#{CC})?#{VV}#{CC}/o
MEQ1 =
cc]vvcc[vv

is m=1

/^(#{CC})?#{VV}#{CC}(#{VV})?$/o
MGR1 =

[cc]vvccvvcc… is m>1

/^(#{CC})?#{VV}#{CC}#{VV}#{CC}/o
VOWEL_IN_STEM =

vowel in stem

/^(#{CC})?#{V}/o

Class Method Summary collapse

Class Method Details

.stem(word) ⇒ Object 



82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
 
# File 'lib/text/porter_stemming.rb', line 82

def self.stem(word)

  # make a copy of the given object and convert it to a string.
  word = word.dup.to_str

  return word if word.length < 3

  # now map initial y to Y so that the patterns never treat it as vowel
  word[0] = 'Y' if word[0] == ?y

  # Step 1a
  if word =~ /(ss|i)es$/
    word = $` + $1
  elsif word =~ /([^s])s$/
    word = $` + $1
  end

  # Step 1b
  if word =~ /eed$/
    word.chop! if $` =~ MGR0
  elsif word =~ /(ed|ing)$/
    stem = $`
    if stem =~ VOWEL_IN_STEM
      word = stem
      case word
        when /(at|bl|iz)$/             then word << "e"
        when /([^aeiouylsz])\1$/       then word.chop!
        when /^#{CC}#{V}[^aeiouwxy]$/o then word << "e"
      end
    end
  end

  if word =~ /y$/
    stem = $`
    word = stem + "i" if stem =~ VOWEL_IN_STEM
  end

  # Step 2
  if word =~ SUFFIX_1_REGEXP
    stem = $`
    suffix = $1
    # print "stem= " + stem + "\n" + "suffix=" + suffix + "\n"
    if stem =~ MGR0
      word = stem + STEP_2_LIST[suffix]
    end
  end

  # Step 3
  if word =~ /(icate|ative|alize|iciti|ical|ful|ness)$/
    stem = $`
    suffix = $1
    if stem =~ MGR0
      word = stem + STEP_3_LIST[suffix]
    end
  end

  # Step 4
  if word =~ SUFFIX_2_REGEXP
    stem = $`
    if stem =~ MGR1
      word = stem
    end
  elsif word =~ /(s|t)(ion)$/
    stem = $` + $1
    if stem =~ MGR1
      word = stem
    end
  end

  #  Step 5
  if word =~ /e$/
    stem = $`
    if (stem =~ MGR1) ||
        (stem =~ MEQ1 && stem !~ /^#{CC}#{V}[^aeiouwxy]$/o)
      word = stem
    end
  end

  if word =~ /ll$/ && word =~ MGR1
    word.chop!
  end

  # and turn initial Y back to y
  word[0] = 'y' if word[0] == ?Y

  word
end