+++ /dev/null
-# coding: utf-8
-
-# Implementation of the Porter 2 stemmer. String#porter2_stem is the main stemming procedure.
-
-class String
- # Tidy up the word before we get down to the algorithm
- def porter2_tidy
- preword = self.to_s.strip.downcase
-
- # map apostrophe-like characters to apostrophes
- preword.gsub!(/‘/, "'")
- preword.gsub!(/’/, "'")
-
- preword
- end
-
-
- # Preprocess the word.
- # Remove any initial ', if present. Then, set initial y, or y after a vowel, to Y
- #
- # (The comment to 'establish the regions R1 and R2' in the original description
- # is an implementation optimisation that identifies where the regions start. As
- # no modifications are made to the word that affect those positions, you may want
- # to cache them now. This implementation doesn't do that.)
- def porter2_preprocess
- w = self.dup
-
- # remove any initial apostrophe
- w.gsub!(/^'*(.)/, '\1')
-
- # set initial y, or y after a vowel, to Y
- w.gsub!(/^y/, "Y")
- w.gsub!(/(#{Porter2::V})y/, '\1Y')
-
- w
- end
-
-
- # R1 is the portion of the word after the first non-vowel after the first vowel
- # (with words beginning 'gener-', 'commun-', and 'arsen-' treated as special cases
- def porter2_r1
- if self =~ /^(gener|commun|arsen)(?<r1>.*)/
- Regexp.last_match(:r1)
- else
- self =~ /#{Porter2::V}#{Porter2::C}(?<r1>.*)$/
- Regexp.last_match(:r1) || ""
- end
- end
-
-
- # R2 is the portion of R1 (porter2_r1) after the first non-vowel after the first vowel
- def porter2_r2
- self.porter2_r1 =~ /#{Porter2::V}#{Porter2::C}(?<r2>.*)$/
- Regexp.last_match(:r2) || ""
- end
-
-
- # Returns true if the word ends with a short syllable
- def porter2_ends_with_short_syllable?
- self =~ /#{Porter2::SHORT_SYLLABLE}$/ ? true : false
- end
-
-
- # A word is short if it ends in a short syllable, and R1 is null
- def porter2_is_short_word?
- self.porter2_ends_with_short_syllable? and self.porter2_r1.empty?
- end
-
-
- # Search for the longest among the suffixes,
- # * '
- # * 's
- # * 's'
- # and remove if found.
- def porter2_step0
- self.sub!(/(.)('s'|'s|')$/, '\1') || self
- end
-
-
- # Search for the longest among the following suffixes, and perform the action indicated.
- # sses:: replace by ss
- # ied, ies:: replace by i if preceded by more than one letter, otherwise by ie
- # s:: delete if the preceding word part contains a vowel not immediately before the s
- # us, ss:: do nothing
- def porter2_step1a
- if self =~ /sses$/
- self.sub(/sses$/, 'ss')
- elsif self =~ /..(ied|ies)$/
- self.sub(/(ied|ies)$/, 'i')
- elsif self =~ /(ied|ies)$/
- self.sub(/(ied|ies)$/, 'ie')
- elsif self =~ /(us|ss)$/
- self
- elsif self =~ /s$/
- if self =~ /(#{Porter2::V}.+)s$/
- self.sub(/s$/, '')
- else
- self
- end
- else
- self
- end
- end
-
-
- # Search for the longest among the following suffixes, and perform the action indicated.
- # eed, eedly:: replace by ee if the suffix is also in R1
- # ed, edly, ing, ingly:: delete if the preceding word part contains a vowel and,
- # after the deletion:
- # * if the word ends at, bl or iz: add e, or
- # * if the word ends with a double: remove the last letter, or
- # * if the word is short: add e
- #
- # (If gb_english is +true+, treat the 'is' suffix as 'iz' above.)
- def porter2_step1b(gb_english = false)
- if self =~ /(eed|eedly)$/
- if self.porter2_r1 =~ /(eed|eedly)$/
- self.sub(/(eed|eedly)$/, 'ee')
- else
- self
- end
- else
- w = self.dup
- if w =~ /#{Porter2::V}.*(ed|edly|ing|ingly)$/
- w.sub!(/(ed|edly|ing|ingly)$/, '')
- if w =~ /(at|lb|iz)$/
- w += 'e'
- elsif w =~ /is$/ and gb_english
- w += 'e'
- elsif w =~ /#{Porter2::Double}$/
- w.chop!
- elsif w.porter2_is_short_word?
- w += 'e'
- end
- end
- w
- end
- end
-
-
- # Replace a suffix of y or Y by i if it is preceded by a non-vowel which is
- # not the first letter of the word.
- def porter2_step1c
- if self =~ /.+#{Porter2::C}(y|Y)$/
- self.sub(/(y|Y)$/, 'i')
- else
- self
- end
- end
-
-
- # Search for the longest among the suffixes listed in the keys of Porter2::STEP_2_MAPS.
- # If one is found and that suffix occurs in R1, replace it with the value
- # found in STEP_2_MAPS.
- #
- # (Suffixes 'ogi' and 'li' are treated as special cases in the procedure.)
- #
- # (If gb_english is +true+, replace the 'iser' and 'isation' suffixes with
- # 'ise', similarly to how 'izer' and 'ization' are treated.)
- def porter2_step2(gb_english = false)
- r1 = self.porter2_r1
- s2m = Porter2::STEP_2_MAPS.dup
- if gb_english
- s2m["iser"] = "ise"
- s2m["isation"] = "ise"
- end
- step_2_re = Regexp.union(s2m.keys.map {|r| Regexp.new(r + "$")})
- if self =~ step_2_re
- if r1 =~ /#{$&}$/
- self.sub(/#{$&}$/, s2m[$&])
- else
- self
- end
- elsif r1 =~ /li$/ and self =~ /(#{Porter2::Valid_LI})li$/
- self.sub(/li$/, '')
- elsif r1 =~ /ogi$/ and self =~ /logi$/
- self.sub(/ogi$/, 'og')
- else
- self
- end
- end
-
-
- # Search for the longest among the suffixes listed in the keys of Porter2::STEP_3_MAPS.
- # If one is found and that suffix occurs in R1, replace it with the value
- # found in STEP_3_MAPS.
- #
- # (Suffix 'ative' is treated as a special case in the procedure.)
- #
- # (If gb_english is +true+, replace the 'alise' suffix with
- # 'al', similarly to how 'alize' is treated.)
- def porter2_step3(gb_english = false)
- if self =~ /ative$/ and self.porter2_r2 =~ /ative$/
- self.sub(/ative$/, '')
- else
- s3m = Porter2::STEP_3_MAPS.dup
- if gb_english
- s3m["alise"] = "al"
- end
- step_3_re = Regexp.union(s3m.keys.map {|r| Regexp.new(r + "$")})
- r1 = self.porter2_r1
- if self =~ step_3_re and r1 =~ /#{$&}$/
- self.sub(/#{$&}$/, s3m[$&])
- else
- self
- end
- end
- end
-
-
- # Search for the longest among the suffixes listed in the keys of Porter2::STEP_4_MAPS.
- # If one is found and that suffix occurs in R2, replace it with the value
- # found in STEP_4_MAPS.
- #
- # (Suffix 'ion' is treated as a special case in the procedure.)
- #
- # (If gb_english is +true+, delete the 'ise' suffix if found.)
- def porter2_step4(gb_english = false)
- if self.porter2_r2 =~ /ion$/ and self =~ /(s|t)ion$/
- self.sub(/ion$/, '')
- else
- s4m = Porter2::STEP_4_MAPS.dup
- if gb_english
- s4m["ise"] = ""
- end
- step_4_re = Regexp.union(s4m.keys.map {|r| Regexp.new(r + "$")})
- r2 = self.porter2_r2
- if self =~ step_4_re
- if r2 =~ /#{$&}/
- self.sub(/#{$&}$/, s4m[$&])
- else
- self
- end
- else
- self
- end
- end
- end
-
-
- # Search for the the following suffixes, and, if found, perform the action indicated.
- # e:: delete if in R2, or in R1 and not preceded by a short syllable
- # l:: delete if in R2 and preceded by l
- def porter2_step5
- if self =~ /ll$/ and self.porter2_r2 =~ /l$/
- self.sub(/ll$/, 'l')
- elsif self =~ /e$/ and self.porter2_r2 =~ /e$/
- self.sub(/e$/, '')
- else
- r1 = self.porter2_r1
- if self =~ /e$/ and r1 =~ /e$/ and not self =~ /#{Porter2::SHORT_SYLLABLE}e$/
- self.sub(/e$/, '')
- else
- self
- end
- end
- end
-
-
- # Turn all Y letters into y
- def porter2_postprocess
- self.gsub(/Y/, 'y')
- end
-
- public
-
- # Perform the stemming procedure. If +gb_english+ is true, treat '-ise' and similar suffixes
- # as '-ize' in American English.
- def porter2_stem(gb_english = false)
- preword = self.porter2_tidy
- return preword if preword.length <= 2
-
- word = preword.porter2_preprocess
-
- if Porter2::SPECIAL_CASES.has_key? word
- Porter2::SPECIAL_CASES[word]
- else
- w1a = word.porter2_step0.porter2_step1a
- if Porter2::STEP_1A_SPECIAL_CASES.include? w1a
- w1a
- else
- w1a.porter2_step1b(gb_english).porter2_step1c.porter2_step2(gb_english).porter2_step3(gb_english).porter2_step4(gb_english).porter2_step5.porter2_postprocess
- end
- end
- end
-
- # A verbose version of porter2_stem that prints the output of each stage to STDOUT
- def porter2_stem_verbose(gb_english = false)
- preword = self.porter2_tidy
- puts "Preword: #{preword}"
- return preword if preword.length <= 2
-
- word = preword.porter2_preprocess
- puts "Preprocessed: #{word}"
-
- if Porter2::SPECIAL_CASES.has_key? word
- puts "Returning #{word} as special case #{Porter2::SPECIAL_CASES[word]}"
- Porter2::SPECIAL_CASES[word]
- else
- r1 = word.porter2_r1
- r2 = word.porter2_r2
- puts "R1 = #{r1}, R2 = #{r2}"
-
- w0 = word.porter2_step0 ; puts "After step 0: #{w0} (R1 = #{w0.porter2_r1}, R2 = #{w0.porter2_r2})"
- w1a = w0.porter2_step1a ; puts "After step 1a: #{w1a} (R1 = #{w1a.porter2_r1}, R2 = #{w1a.porter2_r2})"
-
- if Porter2::STEP_1A_SPECIAL_CASES.include? w1a
- puts "Returning #{w1a} as 1a special case"
- w1a
- else
- w1b = w1a.porter2_step1b(gb_english) ; puts "After step 1b: #{w1b} (R1 = #{w1b.porter2_r1}, R2 = #{w1b.porter2_r2})"
- w1c = w1b.porter2_step1c ; puts "After step 1c: #{w1c} (R1 = #{w1c.porter2_r1}, R2 = #{w1c.porter2_r2})"
- w2 = w1c.porter2_step2(gb_english) ; puts "After step 2: #{w2} (R1 = #{w2.porter2_r1}, R2 = #{w2.porter2_r2})"
- w3 = w2.porter2_step3(gb_english) ; puts "After step 3: #{w3} (R1 = #{w3.porter2_r1}, R2 = #{w3.porter2_r2})"
- w4 = w3.porter2_step4(gb_english) ; puts "After step 4: #{w4} (R1 = #{w4.porter2_r1}, R2 = #{w4.porter2_r2})"
- w5 = w4.porter2_step5 ; puts "After step 5: #{w5}"
- wpost = w5.porter2_postprocess ; puts "After postprocess: #{wpost}"
- wpost
- end
- end
- end
-
- alias stem porter2_stem
-
-end
-
projects / porter2stemmer.git / blobdiff