| Class | String |
| In: |
lib/porter2stemmer/implementation.rb
|
| Parent: | Object |
Implementation of the Porter 2 stemmer. String#porter2_stem is the main stemming procedure.
Returns true if the word ends with a short syllable
# File lib/porter2stemmer/implementation.rb, line 59 def porter2_ends_with_short_syllable? self =~ /#{Porter2::SHORT_SYLLABLE}$/ ? true : false end
A word is short if it ends in a short syllable, and R1 is null
# File lib/porter2stemmer/implementation.rb, line 65 def porter2_is_short_word? self.porter2_ends_with_short_syllable? and self.porter2_r1.empty? end
Turn all Y letters into y
# File lib/porter2stemmer/implementation.rb, line 261 def porter2_postprocess self.gsub(/Y/, 'y') end
Preprocess the word. Remove any initial ’, if present. Then, set initial y, or y after a vowel, to Y
(The comment to ‘establish the regions R1 and R2’ in the original description is an implementation optimisation that identifies where the regions start. As no modifications are made to the word that affect those positions, you may want to cache them now. This implementation doesn‘t do that.)
# File lib/porter2stemmer/implementation.rb, line 25 def porter2_preprocess w = self.dup # remove any initial apostrophe w.gsub!(/^'*(.)/, '\1') # set initial y, or y after a vowel, to Y w.gsub!(/^y/, "Y") w.gsub!(/(#{Porter2::V})y/, '\1Y') w end
R1 is the portion of the word after the first non-vowel after the first vowel (with words beginning ‘gener-’, ‘commun-’, and ‘arsen-’ treated as special cases
# File lib/porter2stemmer/implementation.rb, line 41 def porter2_r1 if self =~ /^(gener|commun|arsen)(?<r1>.*)/ Regexp.last_match(:r1) else self =~ /#{Porter2::V}#{Porter2::C}(?<r1>.*)$/ Regexp.last_match(:r1) || "" end end
R2 is the portion of R1 (porter2_r1) after the first non-vowel after the first vowel
# File lib/porter2stemmer/implementation.rb, line 52 def porter2_r2 self.porter2_r1 =~ /#{Porter2::V}#{Porter2::C}(?<r2>.*)$/ Regexp.last_match(:r2) || "" end
Perform the stemming procedure. If gb_english is true, treat ’-ise’ and similar suffixes as ’-ize’ in American English.
# File lib/porter2stemmer/implementation.rb, line 269 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
# File lib/porter2stemmer/implementation.rb, line 288 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
Search for the longest among the suffixes,
and remove if found.
# File lib/porter2stemmer/implementation.rb, line 75 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 |
# File lib/porter2stemmer/implementation.rb, line 85 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 gb_english is true, treat the ‘is’ suffix as ‘iz’ above.)
# File lib/porter2stemmer/implementation.rb, line 115 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.
# File lib/porter2stemmer/implementation.rb, line 143 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.)
# File lib/porter2stemmer/implementation.rb, line 160 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.)
# File lib/porter2stemmer/implementation.rb, line 192 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[$&]) else self end end end
Search for the longest among the suffixes listed in the keys of Porter2::STEP_4_MAPS. If one is found and that suffix occurs in R2, replace it with the value found in STEP_4_MAPS.
(Suffix ‘ion’ is treated as a special case in the procedure.)
(If gb_english is true, delete the ‘ise’ suffix if found.)
# File lib/porter2stemmer/implementation.rb, line 218 def porter2_step4(gb_english = false) if self.porter2_r2 =~ /ion$/ 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[$&]) else self end else self end end end
Search for the the following suffixes, and, if found, perform the action indicated.
| e: | delete if in R2, or in R1 and not preceded by a short syllable |
| l: | delete if in R2 and preceded by l |
# File lib/porter2stemmer/implementation.rb, line 244 def porter2_step5 if self =~ /ll$/ 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