Measure the distance between two strings with Ruby?

Question

Can I measure the distance between two strings with Ruby?

I.e.:

compare(\'Test\', \'est\') # Returns 1
compare(\'Test\', \'Tes\') #          


        

Answer 1

I like DigitalRoss' solution above. However, as pointed out by dawg, its runtime grows on the order O(3^n), which is no good for longer strings. That solution can be sped up significantly using memoization, or 'dynamic programming':

def lev(string1, string2, memo={})
  return memo[[string1, string2]] if memo[[string1, string2]]
  return string2.size if string1.empty?
  return string1.size if string2.empty?
  min = [ lev(string1.chop, string2, memo) + 1,
          lev(string1, string2.chop, memo) + 1,
          lev(string1.chop, string2.chop, memo) + (string1[-1] == string2[-1] ? 0 : 1)
       ].min
  memo[[string1, string2]] = min
  min
end

We then have much better runtime, (I think it's almost linear? I'm not really sure).

[9] pry(main)> require 'benchmark'
=> true
[10] pry(main)> @memo = {}
=> {}
[11] pry(main)> Benchmark.realtime{puts lev("Hello darkness my old friend", "I've come to talk with you again")}
26
=> 0.007071999832987785