| Class | -String | -
| In: | -
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- lib/porter2stemmer/implementation.rb
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- - |
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| 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:
-
-
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-(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 --
-Tidy up the word before we get down to the algorithm -
- --# File lib/porter2stemmer/implementation.rb, line 7 - def porter2_tidy - preword = self.to_s.strip.downcase - - # map apostrophe-like characters to apostrophes - preword.gsub!(/â/, "'") - preword.gsub!(/â/, "'") - - preword - end --