From aa153bc68c2bf99dd1d75c3486ab795f4bd75ade Mon Sep 17 00:00:00 2001
From: Gibheer <gibheer@gmail.com>
Date: Fri, 10 Jun 2011 00:40:03 +0200
Subject: [PATCH] added an abstract stemmer and an implementation of a simple
 stemmer

---
 lib/polecat.rb                   |  1 +
 lib/polecat/stemmer.rb           | 25 ++++++++++++++++++++++
 lib/polecat/stemmer/simple.rb    | 18 ++++++++++++++++
 spec/simple_stemmer/new_spec.rb  | 12 +++++++++++
 spec/simple_stemmer/stem_spec.rb | 36 ++++++++++++++++++++++++++++++++
 spec/stemmer/new_spec.rb         |  8 +++++++
 spec/stemmer/stem_spec.rb        | 13 ++++++++++++
 7 files changed, 113 insertions(+)
 create mode 100644 lib/polecat/stemmer.rb
 create mode 100644 lib/polecat/stemmer/simple.rb
 create mode 100644 spec/simple_stemmer/new_spec.rb
 create mode 100644 spec/simple_stemmer/stem_spec.rb
 create mode 100644 spec/stemmer/new_spec.rb
 create mode 100644 spec/stemmer/stem_spec.rb

diff --git a/lib/polecat.rb b/lib/polecat.rb
index 2204385..a15bbcc 100644
--- a/lib/polecat.rb
+++ b/lib/polecat.rb
@@ -8,4 +8,5 @@ module Polecat
   require 'polecat/index_searcher'
   require 'polecat/query'
   require 'polecat/term'
+  require 'polecat/stemmer'
 end
diff --git a/lib/polecat/stemmer.rb b/lib/polecat/stemmer.rb
new file mode 100644
index 0000000..e057f75
--- /dev/null
+++ b/lib/polecat/stemmer.rb
@@ -0,0 +1,25 @@
+module Polecat
+  # abstract class for stemmer
+  #
+  # This class can be used for inheritence for your own stemmer.
+  # A stemmer is responsible to convert an document into an array of fragments
+  # which then merged with the index. As every document can be built of
+  # different words and fragments, the stemmer is very important to get the
+  # best result when searching.
+  #
+  # Be warned, that you use the same stemmer for the index as for the search
+  # input!
+  #
+  # To build your own stemmer implement the methods #stem and #result.
+  class Stemmer
+    # stems the word
+    #
+    # This method changes the word into a form, which get's interted into the
+    # index.
+    # @param [Object] word word to stem
+    # @return [Object] the stemmed variant of the word or the same object
+    def stem word
+      raise NotImplementedError, 'please implement #stem'
+    end
+  end
+end
diff --git a/lib/polecat/stemmer/simple.rb b/lib/polecat/stemmer/simple.rb
new file mode 100644
index 0000000..dbeacf1
--- /dev/null
+++ b/lib/polecat/stemmer/simple.rb
@@ -0,0 +1,18 @@
+module Polecat
+  # simple stemmer for cleaning in a simple way
+  #
+  # This class can be used for cleaning strings in the most simple way. If it
+  # does not do, what you intent it to do, inherit from Polecat::Stemmer and
+  # implement your own.
+  class SimpleStemmer < Polecat::Stemmer
+    def stem word
+      if word.class == Array
+        word.each {|w| self.stem w }
+      elsif word.class == String && word.length > 1
+        word.gsub /(ing|ed)$/, ''
+      else
+        word
+      end
+    end
+  end
+end
diff --git a/spec/simple_stemmer/new_spec.rb b/spec/simple_stemmer/new_spec.rb
new file mode 100644
index 0000000..0c4536d
--- /dev/null
+++ b/spec/simple_stemmer/new_spec.rb
@@ -0,0 +1,12 @@
+require File.expand_path(File.dirname(__FILE__) + '/../spec_helper')
+require 'polecat/stemmer/simple'
+
+describe Polecat::SimpleStemmer do
+  it "creates a new SimpleStemmer" do
+    subject.class.should be(Polecat::SimpleStemmer)
+  end
+
+  it "is a stemmer" do
+    subject.kind_of?(Polecat::Stemmer).should be(true)
+  end
+end
diff --git a/spec/simple_stemmer/stem_spec.rb b/spec/simple_stemmer/stem_spec.rb
new file mode 100644
index 0000000..a911c4c
--- /dev/null
+++ b/spec/simple_stemmer/stem_spec.rb
@@ -0,0 +1,36 @@
+require File.expand_path(File.dirname(__FILE__) + '/../spec_helper')
+require 'polecat/stemmer/simple'
+
+describe Polecat::SimpleStemmer do
+  it "takes one argument" do
+    subject.method(:stem).arity.should be(1)
+  end 
+
+  it "returns nil if nil was given" do
+    subject.stem(nil).should be(nil)
+  end
+
+  it "returns the word if nothing was done" do
+    subject.stem("a").should == "a"
+  end
+
+  it "deletes 'ing' from the end" do
+    subject.stem("finding").should == "find"
+  end
+
+  it "deletes 'ed' from the word end" do
+    subject.stem("coded").should == "cod"
+  end
+
+  it "returns numbers not as a string" do
+    subject.stem(1).class.should be(Fixnum)
+  end
+
+  it "returns a float not as a string" do
+    subject.stem(1.1).class.should be(Float)
+  end
+
+  it "takes an array and stems every element in it" do
+    subject.stem(['coding'])[0].should == 'coding'
+  end
+end
diff --git a/spec/stemmer/new_spec.rb b/spec/stemmer/new_spec.rb
new file mode 100644
index 0000000..a1c6135
--- /dev/null
+++ b/spec/stemmer/new_spec.rb
@@ -0,0 +1,8 @@
+require File.expand_path(File.dirname(__FILE__) + '/../spec_helper')
+
+describe "Stemmer#new" do
+  it "creates a new stemmer" do
+    s = Polecat::Stemmer.new
+    s.class.should be(Polecat::Stemmer)
+  end
+end
diff --git a/spec/stemmer/stem_spec.rb b/spec/stemmer/stem_spec.rb
new file mode 100644
index 0000000..e2828e5
--- /dev/null
+++ b/spec/stemmer/stem_spec.rb
@@ -0,0 +1,13 @@
+require File.expand_path(File.dirname(__FILE__) + '/../spec_helper')
+
+describe "Stemmer#stem" do
+  let (:s) { Polecat::Stemmer.new }
+
+  it "takes one argument" do
+    s.method(:stem).arity.should == 1
+  end
+
+  it "raises an error, because it's an abstract class" do
+    lambda { s.stem "word" }.should raise_error(NotImplementedError)
+  end
+end