gistfile1.rb

# Initialize to use Indexer object idx.  Also precomputes some
# things that can be computed with a single traversal of the
# document directory.
def initialize(idx)
  @idx = idx
  @m = 0.0
  @c = Hash.new(0.0)
  @idx.each_document do |doc|
    @m += 1
    @c[cat(doc.name)] += 1
  end
  @categories = @c.keys.sort
  @kz = (1/@m) / (@m + 2/@m) # Kohavi zero
end

# From [KBS97]
def kohavi(a,b)
  return @kz if a == @kz and b == @kz

  if a == 0 then
    if b == 0 then
      return @kz
    else
      return (1/b) / (b + 2/b)
    end
  else
    return a / b
  end
end