--- /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