Class: StringMetric::Levenshtein::IterativeWithFullMatrix

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

Class Method Summary collapse

Class Method Details

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



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# File 'lib/string_metric/levenshtein/iterative_with_full_matrix.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 && (m - n).abs >= max_distance
    return max_distance
  end

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

  d = (0..n).map do |i|
    [0] * (m + 1)
  end

  (1..m).each { |j| d[0][j] = j }
  (1..n).each { |i| d[i][0] = i }

  to_column = 0
  (1..m).each do |j|
    (1..n).each do |i|
      if from[j-1] == to[i-1]
        d[i][j] = d[i -1][j-1]
      else
        d[i][j] = [d[i-1][j]   + insertion_cost,    # insertion
                   d[i][j-1]   + deletion_cost,     # deletion
                   d[i-1][j-1] + substitution_cost  # substitution
                  ].min
      end
      to_column = i
    end

    break if max_distance and d[to_column].min > max_distance
  end

  x = d[n][m]
  if max_distance && x > max_distance
    max_distance
  else
    x
  end
end