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SwiftyLevenshtein.swift
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SwiftyLevenshtein.swift
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//
// SwiftyLevenshtein.swift
// Levenshtein distance algorithm written in Swift 2.2. Both a slow and highly optimized version are included.
//
// Created by Mark Hamilton on 3/31/16.
// Copyright © 2016 dryverless. (http://www.dryverless.com)
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//
import Foundation
// Minimize 3
public func min3(a: Int, b: Int, c: Int) -> Int {
return min( min(a, c), min(b, c))
}
// In case they ever let subscripts throw
//public extension String {
//
// internal enum SubscriptError: ErrorType {
//
// case InvalidFirstChar
//
// case InvalidLastChar
//
// }
//
//
// subscript(range: Range<Int>) throws -> String {
//
// guard let firstChar = startIndex.advancedBy(range.startIndex) else {
//
// throw SubscriptError.InvalidFirstChar
// }
//
// guard let lastChar = startIndex.advancedBy(range.endIndex) else {
//
// throw SubscriptError.InvalidLastChar
//
// }
//
// return self[firstChar...<lastChar]
//
//
// }
//
//}
public extension String {
subscript(index: Int) -> Character {
return self[startIndex.advancedBy(index)]
}
subscript(range: Range<Int>) -> String {
let char0 = startIndex.advancedBy(range.startIndex)
let charN = startIndex.advancedBy(range.endIndex)
return self[char0..<charN]
}
}
public struct Array2D {
var columns: Int
var rows: Int
var matrix: [Int]
init(columns: Int, rows: Int) {
self.columns = columns
self.rows = rows
matrix = Array(count:columns*rows, repeatedValue:0)
}
subscript(column: Int, row: Int) -> Int {
get {
return matrix[columns * row + column]
}
set {
matrix[columns * row + column] = newValue
}
}
func columnCount() -> Int {
return self.columns
}
func rowCount() -> Int {
return self.rows
}
}
/* Levenshtein Distance Algorithm
* Calculates the minimum number of changes (distance) between two strings.
*/
public func slowlevenshtein(sourceString: String, target targetString: String) -> Int {
let targetLength = targetString.characters.count
let sourceLength = sourceString.characters.count
guard targetLength > 0 && sourceLength > 0 else { return max(targetLength, sourceLength) }
let source = Array(sourceString.unicodeScalars)
let target = Array(targetString.unicodeScalars)
var matrix = Array(count: targetLength + 1, repeatedValue: Array(count: sourceLength + 1, repeatedValue: 0))
for x in 1..<targetLength {
matrix[x][0] = matrix[x - 1][0] + 1
}
for y in 1..<sourceLength {
matrix[0][y] = matrix[0][y - 1] + 1
}
for x in 1..<(targetLength + 1) {
for y in 1..<(sourceLength + 1) {
let penalty = source[y - 1] == target[x - 1] ? 0 : 1
let (deletions, insertions, substitutions) = (matrix[x - 1][y] + 1, matrix[x][y - 1] + 1, matrix[x - 1][y - 1])
matrix[x][y] = min3(deletions, b: insertions, c: substitutions + penalty)
}
}
return matrix[targetLength][sourceLength]
}
public func levenshtein(sourceString: String, target targetString: String) -> Int {
let targetLength = targetString.characters.count
let sourceLength = sourceString.characters.count
guard targetLength > 0 && sourceLength > 0 else { return max(targetLength, sourceLength) }
let source = Array(sourceString.unicodeScalars)
let target = Array(targetString.unicodeScalars)
var distance = Array2D(columns: sourceLength + 1, rows: targetLength + 1)
for x in 1...sourceLength {
distance[x, 0] = x
}
for y in 1...targetLength {
distance[0, y] = y
}
for x in 1...sourceLength {
for y in 1...targetLength {
if source[x - 1] == target[y - 1] {
// no difference
distance[x, y] = distance[x - 1, y - 1]
} else {
distance[x, y] = min3(
// deletions
distance[x - 1, y] + 1,
// insertions
b: distance[x, y - 1] + 1,
// substitutions
c: distance[x - 1, y - 1] + 1
)
}
}
}
return distance[source.count, target.count]
}
public extension String {
func getSlowLevenshtein(target: String) -> Int {
return slowlevenshtein(self, target: target)
}
func getLevenshtein(target: String) -> Int {
return levenshtein(self, target: target)
}
}