Calculate edit distances and edit scripts between vectors.

An implementation of the Wagner–Fischer dynamic programming algorithm to find the optimal edit script and cost between two sequences.

The implementation in this package is specialised to sequences represented with Data.Vector but is otherwise agnostic to:

• The type of values in the vectors;

• The type representing edit operations; and

• The type representing the cost of operations.

Edit Distance: Vector

This is a small library for calculating the edit distance and edit script between two vectors. It is generic enough that you should be able to use it with vectors containing values of any type you like, with changes described by any type you like, and with costs represented by any type you like (with a few restrictions).

Installing

The edit-distance-vector package is a normal Haskell library and can be installed using the Cabal package management tool.

cabal update
cabal install edit-distance-vector

edit-distance-vector is automatically tested on GHC versions 7.4.2, 7.6.3, 7.8.3, 7.10.1, 8.0.2 using the Travis CI service.

Usage

The interface to edit-distance-vector is very small; just import Data.Vector.Distance, create a Params value with the correct operations to deal with your types, and pass this to leastChanges along with your Vectors.

import           Data.Monoid

import qualified Data.Vector          as V
import           Data.Vector.Distance

-- | Editing vectors of 'Char' values, with '(String, Int, Char)' describing
--   changes, and the additive monoid of 'Int' describing costs.
str :: Params Char (String, Int, Char) (Sum Int)
str = Params
    { equivalent = (==)
    , delete     = \i c    -> ("delete", i, c)
    , insert     = \i c    -> ("insert", i, c)
    , substitute = \i c c' -> ("replace", i, c')
    , cost = const (Sum 1)
    , positionOffset = \ (op, _, _) -> if op == "delete" then 0 else 1
    }

main :: IO ()
main = do
    print $ leastChanges str (V.fromList "I am thomas")
                             (V.fromList "My name is Thomas")

(See test/sample.hs for a version of this code that is compiled by the automated test suite.)