basic edits for Strings

edits.rb

# useful for things like http://norvig.com/spell-correct.html

module Edits
  
  DICT = { "cap" => 1, "carp" => 1, "clap" => 1, "cramp" => 1 }
  
  def deletes
    map_transforms { |word, i| word.delete_at(i) }
  end
  
  def transposes
    map_transforms { |word, i| word[i], word[i+1] = word[i+1], word[i] }
  end
  
  def replaces
    ("a".."z").map do |c|
      map_transforms { |word, i| word[i] = c }
    end.flatten
  end
  
  def inserts
    ("a".."z").map do |c|
      r = map_transforms { |word, i| word.insert(i, c) }
      terminal = "#{self}#{c}"
      r << terminal if terminal.score
      r
    end.flatten
  end
  
  def map_transforms
    out = []
    chars = self.split('')
    self.size.times do |i|
      yield(word = chars.dup, i)
      word = word.join
      out << word if word.score && word != self
    end
    out
  end
  
  def score
    DICT[self]
  end
  
end

String.send(:include, Edits)

describe "a String, imbued with Edits" do
  
  it "works" do
    r = "crap".deletes
    r.should == %w{ cap }
    
    r = "crap".transposes
    r.should == %w{ carp }
    
    r = "crap".replaces
    r.should == %w{ clap }
    
    r = "crap".inserts
    r.should == %w{ cramp }
  end

  
end