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Edit Distance

An Elm package for calculating between-list edit distances.

It can calculate both the Levenshtein distance between two lists and the actual edit steps required to go from one list to another (using the Wagner-Fischer algorithm).

-- Levenshtein.
levenshtein (String.toList "kitten") (String.toList "sitting") == 3
levenshteinFromStrings "garvey" "avery" == 3

-- Edit steps.
edits (String.toList "kitten") (String.toList "sitting") ==
  [ Substitute 's' 0
  , Substitute 'i' 4
  , Insert 'g' 6
  ]

editsFromStrings "sitting" "kitten" ==
  [ Substitute 'k' 0
  , Substitute 'e' 4
  , Delete 'g' 6
  ]

-- Edit steps include moves (i.e. deletions followed by insertions).
editsFromStrings "garvey" "avery" ==
  [ Delete 'g' 0
  , Move 'r' 2 3
  ]

The resulting indices reflect edits where deletions are made first, before insertions and substitutions. That is, indices for deletions refer to the source list, whereas indices for insertions and substitutions refer to the latter, intermediate lists.

An example will serve. Calling editsFromStrings with "preterit" and "zeitgeist" returns the following:

[ Substitute 'z' 0
, Delete 'r' 1
, Insert 'i' 2
, Insert 'g' 4
, Delete 'r' 5
, Insert 's' 7
]

Let's look at these steps in order, keeping in mind that deletions are made first:

  1. Deleting at index 1 in "preterit" gives "peterit".
  2. Deleting at index 5 in "preterit" gives "peteit".
  3. Substituting "z" at index 0 in "peteit" gives "zeteit".
  4. Inserting "i" at index 2 in "zeteit" gives "zeiteit".
  5. Inserting "g" at index 4 in "zeiteit" gives "zeitgeit".
  6. Inserting "s" at index 7 in "zeitgeit" gives "zeitgeist".

To do

  • String support.
  • Custom cost function.
  • Memoization.

Tests

First install elm-test:

$ npm install -g elm-test

Then run the tests, and you should see something like this:

$ elm-test
Success! Compiled 1 module.
Successfully generated /var/folders/kb/lmdz_h5n629b85bbnkxhfx3c0000gn/T/elm_test_1161113-40357-1bh5q3m.e262a3v7vi.js

elm-test
--------

Running 26 tests. To reproduce these results, run: elm-test --seed 514474818


TEST RUN PASSED

Duration: 796 ms
Passed:   26
Failed:   0

Contributing

Contributions are welcome. Just open up an issue if you've found a problem or have a suggestion for a feature, or a pull request if you already know how to fix or implement it.

Change Log

1.1.1

  • Update for Elm 0.18.

1.1.0

  • Adds support for custom cost functions in the form of editsWithCostFunc and editsWithCostFuncFromStrings.

1.0.0

  • Initial version, with support for calculating Levenshtein distance and edit steps using the Wagner-Fischer algorithm. Also includes String support.