Class: StringMetric::Levenshtein::IterativeWithTwoMatrixRows

Inherits:
Object
  • Object
show all
Defined in:
lib/string_metric/levenshtein/iterative_with_two_matrix_rows.rb

Class Method Summary collapse

Class Method Details

.distance(from, to, options = {}) ⇒ Object 



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# File 'lib/string_metric/levenshtein/iterative_with_two_matrix_rows.rb', line 6

def self.distance(from, to, options = {})
  max_distance      = options[:max_distance]
  insertion_cost    = options.fetch(:insertion_cost, 1)
  deletion_cost     = options.fetch(:deletion_cost, 1)
  substitution_cost = options.fetch(:substitution_cost, 1)

  m = from.length
  n = to.length

  if max_distance && (n - m).abs >= max_distance
    return max_distance
  end

  return 0 if from == to
  return n if m.zero?
  return m if n.zero?

  v0 = (0..m).to_a
  x = 0

  n.times do |i|
    current = x = i + 1
    sub_cell = v0[0]

    m.times do |j|
      cost = (from[j] == to[i]) ? 0 : substitution_cost

      ins_cell = v0[j+1]

      x = [current + deletion_cost,   # deletion
           ins_cell + insertion_cost, # insertion
           sub_cell + cost            # substitution
          ].min

      v0[j] = current
      current = x
      sub_cell = ins_cell
    end

    v0[m] = x
    break if max_distance && v0.min > max_distance
  end

  if max_distance && x > max_distance
    max_distance
  else
    x
  end
end