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#
# This is the Porter Stemming algorithm, ported to Ruby from the
# version coded up in Perl. It's easy to follow against the rules
# in the original paper in:
#
# Porter, 1980, An algorithm for suffix stripping, Program, Vol. 14,
# no. 3, pp 130-137,
#
# Taken from http://www.tartarus.org/~martin/PorterStemmer (Public Domain)
#
module Text # :nodoc:
module PorterStemming
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 = "[^aeiou]" # consonant
V = "[aeiouy]" # vowel
CC = "#{C}(?>[^aeiouy]*)" # consonant sequence
VV = "#{V}(?>[aeiou]*)" # vowel sequence
MGR0 = /^(#{CC})?#{VV}#{CC}/o # [cc]vvcc... is m>0
MEQ1 = /^(#{CC})?#{VV}#{CC}(#{VV})?$/o # [cc]vvcc[vv] is m=1
MGR1 = /^(#{CC})?#{VV}#{CC}#{VV}#{CC}/o # [cc]vvccvvcc... is m>1
VOWEL_IN_STEM = /^(#{CC})?#{V}/o # vowel in stem
def self.stem(word)
# make a copy of the given object and convert it to a string.
word = word.dup.to_str
return word if word.length < 3
# now map initial y to Y so that the patterns never treat it as vowel
word[0] = 'Y' if word[0] == ?y
# Step 1a
if word =~ /(ss|i)es$/
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
end
end
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