Levenshtein distance in Swift3 - swift

Question

I'm using a tutorial from Rosetta Code to calculate Levenshtein distance. It seems their code is in Swift2 so I get this error Binary operator '+' cannot be applied to operands of type '[Int]' and 'Repeated<String.CharacterView>' when doing this: var cur = [i + 2] + empty where let empty = repeatElement(s, count: 0). How can I go about this?

Answer 1

There were a couple of changes to make.
The construction of the Array empty.
enumerate() is now enumerated()
successor() doesn't exist anymore so I replaced it with +1
So the function is now
Swift 4:
func levDis(_ w1: String, _ w2: String) -> Int {
let empty = [Int](repeating:0, count: w2.count)
var last = [Int](0...w2.count)
for (i, char1) in w1.enumerated() {
var cur = [i + 1] + empty
for (j, char2) in w2.enumerated() {
cur[j + 1] = char1 == char2 ? last[j] : min(last[j], last[j + 1], cur[j]) + 1
}
last = cur
}
return last.last!
}
Swift 3:
func levDis(w1: String, w2: String) -> Int {
let (t, s) = (w1.characters, w2.characters)
let empty = Array<Int>(repeating:0, count: s.count)
var last = [Int](0...s.count)
for (i, tLett) in t.enumerated() {
var cur = [i + 1] + empty
for (j, sLett) in s.enumerated() {
cur[j + 1] = tLett == sLett ? last[j] : min(last[j], last[j + 1], cur[j])+1
}
last = cur
}
return last.last!
}

Answer 2

Updated and improved answer to Swift 4, based on #Spads answer.
extension String {
func levenshteinDistanceScore(to string: String, ignoreCase: Bool = true, trimWhiteSpacesAndNewLines: Bool = true) -> Float {
var firstString = self
var secondString = string
if ignoreCase {
firstString = firstString.lowercased()
secondString = secondString.lowercased()
}
if trimWhiteSpacesAndNewLines {
firstString = firstString.trimmingCharacters(in: .whitespacesAndNewlines)
secondString = secondString.trimmingCharacters(in: .whitespacesAndNewlines)
}
let empty = [Int](repeating:0, count: secondString.count)
var last = [Int](0...secondString.count)
for (i, tLett) in firstString.enumerated() {
var cur = [i + 1] + empty
for (j, sLett) in secondString.enumerated() {
cur[j + 1] = tLett == sLett ? last[j] : Swift.min(last[j], last[j + 1], cur[j])+1
}
last = cur
}
// maximum string length between the two
let lowestScore = max(firstString.count, secondString.count)
if let validDistance = last.last {
return 1 - (Float(validDistance) / Float(lowestScore))
}
return 0.0
}
}
infix operator =~
func =~(string: String, otherString: String) -> Bool {
return string.levenshteinDistanceScore(to: otherString) >= 0.85
}

Answer 3

func ~=(string: String, otherString: String) -> Bool {
return string.levenshteinDistanceScore(to: otherString) >= 0.85
}

Answer 4

Since #Daniel Illescas answer is not working, here is working version with Int return type and with assert.
extension String {
func levenshteinDistance(to string: String, ignoreCase: Bool = true, trimWhiteSpacesAndNewLines: Bool = true) -> Int {
var firstString = self
var secondString = string
if ignoreCase {
firstString = firstString.lowercased()
secondString = secondString.lowercased()
}
if trimWhiteSpacesAndNewLines {
firstString = firstString.trimmingCharacters(in: .whitespacesAndNewlines)
secondString = secondString.trimmingCharacters(in: .whitespacesAndNewlines)
}
let empty = [Int](repeating: 0, count: secondString.count)
var last = [Int](0...secondString.count)
for (i, tLett) in firstString.enumerated() {
var cur = [i + 1] + empty
for (j, sLett) in secondString.enumerated() {
cur[j + 1] = tLett == sLett ? last[j] : Swift.min(last[j], last[j + 1], cur[j]) + 1
}
last = cur
}
if let validDistance = last.last {
return validDistance
}
assertionFailure()
return 0
}
}