X-Git-Url: https://git.njae.me.uk/?a=blobdiff_plain;f=lib%2Fporter2.rb;h=229128dc2751237b5cf4701a8a7d9add81d3058a;hb=aa5699112116010af665e83447bd7d1a17d0e2f7;hp=2236b12272ad81b2db73a637176d693406b0c761;hpb=9dd2505747fbbd6040e9516dd0ae2e8ec5c6a4d2;p=porter2stemmer.git diff --git a/lib/porter2.rb b/lib/porter2.rb index 2236b12..229128d 100644 --- a/lib/porter2.rb +++ b/lib/porter2.rb @@ -1,377 +1,8 @@ -# coding: utf-8 - -# Porter 2 stemmer in Ruby. -# -# This is the Porter 2 stemming algorithm, as described at -# http://snowball.tartarus.org/algorithms/english/stemmer.html -# The original paper is: -# -# Porter, 1980, "An algorithm for suffix stripping", _Program_, Vol. 14, -# no. 3, pp 130-137 - -module Stemmable - # A non-vowel - C = "[^aeiouy]" - - # A vowel - V = "[aeiouy]" - - # A non-vowel other than w, x, or Y - CW = "[^aeiouywxY]" - - # Doubles created when added a suffix: these are undoubled when stemmed - Double = "(bb|dd|ff|gg|mm|nn|pp|rr|tt)" - - # A valid letter that can come before 'li' - Valid_LI = "[cdeghkmnrt]" - - # A specification for a short syllable - SHORT_SYLLABLE = "((#{C}#{V}#{CW})|(^#{V}#{C}))" - - # Suffix transformations used in Step 2. - # (ogi, li endings dealt with in procedure) - STEP_2_MAPS = {"tional" => "tion", - "enci" => "ence", - "anci" => "ance", - "abli" => "able", - "entli" => "ent", - "ization" => "ize", - "izer" => "ize", - "ational" => "ate", - "ation" => "ate", - "ator" => "ate", - "alism" => "al", - "aliti" => "al", - "alli" => "al", - "fulness" => "ful", - "ousli" => "ous", - "ousness" => "ous", - "iveness" => "ive", - "iviti" => "ive", - "biliti" => "ble", - "bli" => "ble", - "fulli" => "ful", - "lessli" => "less" } - - # Suffix transformations used in Step 3. - # (ative ending dealt with in procedure) - STEP_3_MAPS = {"tional" => "tion", - "ational" => "ate", - "alize" => "al", - "icate" => "ic", - "iciti" => "ic", - "ical" => "ic", - "ful" => "", - "ness" => "" } - - # Suffix transformations used in Step 4. - STEP_4_MAPS = {"al" => "", - "ance" => "", - "ence" => "", - "er" => "", - "ic" => "", - "able" => "", - "ible" => "", - "ant" => "", - "ement" => "", - "ment" => "", - "ent" => "", - "ism" => "", - "ate" => "", - "iti" => "", - "ous" => "", - "ive" => "", - "ize" => "" } - - # Special-case stemmings - SPECIAL_CASES = {"skis" => "ski", - "skies" => "sky", - - "dying" => "die", - "lying" => "lie", - "tying" => "tie", - "idly" => "idl", - "gently" => "gentl", - "ugly" => "ugli", - "early" => "earli", - "only" => "onli", - "singly" =>"singl", - - "sky" => "sky", - "news" => "news", - "howe" => "howe", - "atlas" => "atlas", - "cosmos" => "cosmos", - "bias" => "bias", - "andes" => "andes" } - - # Special case words to ignore after step 1a. - STEP_1A_SPECIAL_CASES = %w[ inning outing canning herring earring proceed exceed succeed ] - - # 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 - - 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!(/(#{V})y/, '\1Y') - - w - end - - # The word after the first non-vowel after the first vowel - def porter2_r1 - if self =~ /^(gener|commun|arsen)(?.*)/ - Regexp.last_match(:r1) - else - self =~ /#{V}#{C}(?.*)$/ - Regexp.last_match(:r1) || "" - end - end - - # R1 after the first non-vowel after the first vowel - def porter2_r2 - self.porter2_r1 =~ /#{V}#{C}(?.*)$/ - Regexp.last_match(:r2) || "" - end - - # A short syllable in a word is either - # 1. a vowel followed by a non-vowel other than w, x or Y and preceded by a non-vowel, or - # 2. a vowel at the beginning of the word followed by a non-vowel. - def porter2_ends_with_short_syllable? - self =~ /#{SHORT_SYLLABLE}$/ ? true : false - end - - # A word is short if it ends in a short syllable, and if R1 is null - def porter2_is_short_word? - self.porter2_ends_with_short_syllable? and self.porter2_r1.empty? - end - - # Search for the longest among the suffixes, - # * ' - # * 's - # * 's' - # and remove if found. - def step_0 - self.sub!(/(.)('s'|'s|')$/, '\1') || self - end - - # Remove plural suffixes - def step_1a - 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 =~ /(#{V}.+)s$/ - self.sub(/s$/, '') - else - self - end - else - self - end - end - - def step_1b(gb_english = false) - if self =~ /(eed|eedly)$/ - if self.porter2_r1 =~ /(eed|eedly)$/ - self.sub(/(eed|eedly)$/, 'ee') - else - self - end - else - w = self.dup - if w =~ /#{V}.*(ed|edly|ing|ingly)$/ - w.sub!(/(ed|edly|ing|ingly)$/, '') - if w =~ /(at|lb|iz)$/ - w += 'e' - elsif w =~ /is$/ and gb_english - w += 'e' - elsif w =~ /#{Double}$/ - w.chop! - elsif w.porter2_is_short_word? - w += 'e' - end - end - w - end - end - - - def step_1c - if self =~ /.+#{C}(y|Y)$/ - self.sub(/(y|Y)$/, 'i') - else - self - end - end - - - def step_2(gb_english = false) - r1 = self.porter2_r1 - s2m = 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$/ and self =~ /(#{Valid_LI})li$/ - self.sub(/li$/, '') - elsif r1 =~ /ogi$/ and self =~ /logi$/ - self.sub(/ogi$/, 'og') - else - self - end - end - - - def step_3(gb_english = false) - if self =~ /ative$/ and self.porter2_r2 =~ /ative$/ - self.sub(/ative$/, '') - else - s3m = STEP_3_MAPS.dup - if gb_english - s3m["alise"] = "al" - end - step_3_re = Regexp.union(s3m.keys.map {|r| Regexp.new(r + "$")}) - r1 = self.porter2_r1 - if self =~ step_3_re and r1 =~ /#{$&}$/ - self.sub(/#{$&}$/, s3m[$&]) - else - self - end - end - end - - - def step_4(gb_english = false) - if self.porter2_r2 =~ /ion$/ and self =~ /(s|t)ion$/ - self.sub(/ion$/, '') - else - s4m = 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[$&]) - else - self - end - else - self - end - end - end - - - def step_5 - if self =~ /ll$/ 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$/ and not self =~ /#{SHORT_SYLLABLE}e$/ - self.sub(/e$/, '') - else - self - end - end - end - - - def porter2_postprocess - self.gsub(/Y/, 'y') - end - - - def porter2_stem(gb_english = false) - preword = self.porter2_tidy - return preword if preword.length <= 2 - - word = preword.porter2_preprocess - - if SPECIAL_CASES.has_key? word - SPECIAL_CASES[word] - else - w1a = word.step_0.step_1a - if STEP_1A_SPECIAL_CASES.include? w1a - w1a - else - w1a.step_1b(gb_english).step_1c.step_2(gb_english).step_3(gb_english).step_4(gb_english).step_5.porter2_postprocess - end - end - end - - 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 SPECIAL_CASES.has_key? word - puts "Returning #{word} as special case #{SPECIAL_CASES[word]}" - SPECIAL_CASES[word] - else - r1 = word.porter2_r1 - r2 = word.porter2_r2 - puts "R1 = #{r1}, R2 = #{r2}" - - w0 = word.step_0 ; puts "After step 0: #{w0} (R1 = #{w0.porter2_r1}, R2 = #{w0.porter2_r2})" - w1a = w0.step_1a ; puts "After step 1a: #{w1a} (R1 = #{w1a.porter2_r1}, R2 = #{w1a.porter2_r2})" - - if STEP_1A_SPECIAL_CASES.include? w1a - puts "Returning #{w1a} as 1a special case" - w1a - else - w1b = w1a.step_1b(gb_english) ; puts "After step 1b: #{w1b} (R1 = #{w1b.porter2_r1}, R2 = #{w1b.porter2_r2})" - w1c = w1b.step_1c ; puts "After step 1c: #{w1c} (R1 = #{w1c.porter2_r1}, R2 = #{w1c.porter2_r2})" - w2 = w1c.step_2(gb_english) ; puts "After step 2: #{w2} (R1 = #{w2.porter2_r1}, R2 = #{w2.porter2_r2})" - w3 = w2.step_3(gb_english) ; puts "After step 3: #{w3} (R1 = #{w3.porter2_r1}, R2 = #{w3.porter2_r2})" - w4 = w3.step_4(gb_english) ; puts "After step 4: #{w4} (R1 = #{w4.porter2_r1}, R2 = #{w4.porter2_r2})" - w5 = w4.step_5 ; puts "After step 5: #{w5}" - wpost = w5.porter2_postprocess ; puts "After postprocess: #{wpost}" - wpost - end - end - end - - alias stem porter2_stem - -end - -# Add stem method to all Strings -class String - include Stemmable - - # private :porter2_preprocess, :porter2_r1, :porter2_r2 -end +# coding: utf-8 + +# ==The Porter 2 stemmer + +$:.unshift File.join(File.dirname(__FILE__), "..", "lib") +require 'porter2_constants' +require 'porter2_implementation' +