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 = {})
  return 0 if from == to
  return to.size if from.size.zero?
  return from.size if to.size.zero?

  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

  v0 = (0..m).to_a
  v1 = []
  x = 0

  n.times do |i|
    x = v1[0] = i + 1

    sub_cell = v0[0]

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

      ins_cell = v0[j+1]

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


      v1[j + 1] = x

      sub_cell = ins_cell
    end

    break if max_distance && v0[i] > max_distance

    v0 = v1.dup
  end

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