operations.coffee

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operations.coffee

global =
  if typeof exports is 'object'
    exports
  else if typeof window is 'object'
    window
  else
    this

global['levenshtein'] ||= {}
global['levenshtein']['operations'] =
  insertion: (term, alphabet, random) ->

Select a random character to insert

    c = alphabet[(random() * alphabet.length) >> 0]

¶

Select a random index at which to insert the character
```
    i = (random() * (1 + term.length)) >> 0
```

Insert the charater at the random index

    term.slice(0,i) + c + term.slice(1 + i)

  deletion: (term, alphabet, random) ->

¶

Select a random index for deletion
```
    i = (random() * term.length) >> 0
```

Delete the character at the random index

    term.slice(0,i) + term.slice(i+1)

  substitution: (term, alphabet, random) ->

Select a random character to substitute

    c = alphabet[(random() * alphabet.length) >> 0]

¶

Select a random index for substitution
```
    i = (random() * term.length) >> 0
```

Substitute the character at the random index

    term.slice(0,i) + c + term.slice(i+1)

  transposition: (term, alphabet, random) ->
    if term.length > 1

Select a random index to transpose

      i = (random() * (term.length - 1)) >> 0

Transpose the characters at i and i+1

      term.slice(0,i) + term[i+1] + term[i] + term.slice(i+2)
    else
      term

  merge: (term, alphabet, random) ->
    if term.length > 1

Select a random character to merge-in

      c = alphabet[(random() * alphabet.length) >> 0]

Select a random index to merge

      i = (random() * (term.length - 1)) >> 0

Merge the characters at i and i+1

      term.slice(0,i) + c + term.slice(i+2)
    else
      term

  split: (term, alphabet, random) ->

Select two random characters to split-out

    c = alphabet[(random() * alphabet.length) >> 0]
    d = alphabet[(random() * alphabet.length) >> 0]

Select a random index to split

    i = (random() * (term.length - 1)) >> 0

Split the character at i

    term.slice(0,i) + c + d + term.slice(i+1)