d ← L ##.dist R                             ⍝ Levenshtein distance.

From Jay Foad, [dist] returns the "distance" between simple vectors L and R.

The O(m×n) algorithm compares sequences, calculating the minimum number of edits
required to transform one into the other. The notional costs of the edit operat-
ions are:

    Insert item:  1
    Delete item:  1
    Replace item: 1
    Copy item:    0

For example, comparing vectors 'Sunday' and  'Saturday' implies  the  following
table, where each item is:

    0 + its NW neighbour, if the corresponding items match.
    1 + the minimum of its N, W and NW neighbours, otherwise.

      S a t u r d a y
    S 0 1 2 3 4 5 6 7
    u 1 1 2 2 3 4 5 6
    n 2 2 2 3 3 4 5 6
    d 3 3 3 3 4 3 4 5
    a 4 3 4 4 4 4 3 4
    y 5 4 4 5 5 5 4 3

Each number in the table is the edit distance between the sub-strings above  and
to its left.  For example, the 2 in the second  row, fourth column, is the dist-
ance from 'Su' to 'Satu': two copies and two insertions.

Note that, as the cost of insertion  and  deletion  is the same, the function is
commutative. 'Satu' → 'Su' : two copies and two deletions.

The Levenshtein distance between the two sequences is thus the lower-right table
item (3 in the above example).

See: http://en.wikipedia.org/wiki/Levenshtein_distance

Technical note:

    dist←{⎕ML←0                     ⍝ Levenshtein distance.
        a←(n+1)⍴(⍴⍺)+n←⍴⍵           ⍝ first row of matrix
        f←⍵{⌊\⍵⌊(⊃⍵),(¯1↓⍵)-1+⍺=⍺⍺} ⍝ iteration step
        z←⊃f/(⌽⍺),⊂a                ⍝ last row of matrix
        ⊃⌽z
    }

[dist] calculates a row of the matrix at a time.  The / iterates over successive
characters from ⍺, generating a new matrix row each time. The ⌊\ is key to calc-
ulating a whole row quickly.

Examples

    'Sunday' dist 'Saturday'                ⍝ distance between strings.
3
    'sitting' dist 'kitten'                 ⍝ examples from Wikipedia.
3
    mons ← 'January' 'February' 'March'
    mons,← 'April'   'May'      'June'
    mons,← 'July'    'August'   'September'
    mons,← 'October' 'November' 'December'

    mons ∘.dist mons                        ⍝ distances between months
0 4 6 7 5 5 4 6 9 7 8 8
4 0 7 7 6 7 6 7 8 7 8 7
6 7 0 4 3 5 5 6 9 7 8 8
7 7 4 0 5 5 5 5 8 7 8 8
5 6 3 5 0 4 3 6 9 7 8 8
5 7 5 5 4 0 2 5 8 6 7 7
4 6 5 5 3 2 0 5 9 7 8 8
6 7 6 5 6 5 5 0 9 7 8 8
9 8 9 8 9 8 9 9 0 5 4 3
7 7 7 7 7 6 7 7 5 0 5 4
8 8 8 8 8 7 8 8 4 5 0 3
8 7 8 8 8 7 8 8 3 4 3 0

    fuzzy←{({⍵⍳⌊/⍵}(lcase ⍺)∘dist∘lcase¨⍵)⊃⍵}   ⍝ fuzzy selection

    fuzzy∘mons¨ 'dcmbr' 'marching' 'febury'     ⍝ fuzzy matches
 December  March  February

See also: lcase

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