X-Git-Url: https://git.njae.me.uk/?a=blobdiff_plain;f=lib%2Fporter2_implementation.rb;fp=lib%2Fporter2_implementation.rb;h=906f5bd0671d04323655f5383cf85524102bb05d;hb=074ce0bade4a2e3ab2210624ba598cd5edd0bec8;hp=0000000000000000000000000000000000000000;hpb=066fa6953e201272b93df3b32f25fff2e18c4ec7;p=porter2stemmer.git diff --git a/lib/porter2_implementation.rb b/lib/porter2_implementation.rb new file mode 100644 index 0000000..906f5bd --- /dev/null +++ b/lib/porter2_implementation.rb @@ -0,0 +1,326 @@ +# 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)(?.*)/ + Regexp.last_match(:r1) + else + self =~ /#{Porter2::V}#{Porter2::C}(?.*)$/ + Regexp.last_match(:r1) || "" + end + end + + + # R2 is the portion of R1 (porter2_r1) after the first non-vowel after the first vowel + def porter2_r2 + self.porter2_r1 =~ /#{Porter2::V}#{Porter2::C}(?.*)$/ + 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 +