Related
Question:
Given a string, return a new string made of every other char starting with the first, so "Hello" yields "Hlo".
string_bits('Hello') → 'Hlo'
string_bits('Hi') → 'H'
string_bits('Heeololeo') → 'Hello'
Solution:
func string_bits(userString: String) ->String{
var myString = ""
for(i, v) in userString.enumerated(){
if i % 2 == 0{
myString.append(v)
}
}
return myString
}
Output: Hello
Now my question:
Is there any I can iterate my index any way in swift like object-c, c, or other programming languages does. For instance:
result = ""
# On each iteration, add the substring of the chars 0..i
for i in range(len(str)):
result = result + str[:i+1]
return result
str[:i+1]
Here, I am adding +1 with the current index and getting the index value. How can I do this in swift.
extension Collection {
func everyNthIndex(n: Int) -> UnfoldSequence<Index,Index> {
sequence(state: startIndex) { index in
guard index < endIndex else { return nil }
defer { index = self.index(index, offsetBy: n, limitedBy: endIndex) ?? endIndex }
return index
}
}
}
let alphabet = "abcdefghijklmnopqrstuvwxyz"
for evenIndex in alphabet.everyNthIndex(n: 2) {
print("evenIndex", evenIndex, "char:", alphabet[evenIndex])
}
for oddIndex in alphabet.dropFirst().everyNthIndex(n: 2) {
print("oddIndex", oddIndex, "char:", alphabet[oddIndex])
}
regular approach using while loop:
var index = alphabet.startIndex
while index < alphabet.endIndex {
defer { index = alphabet.index(index, offsetBy: 1) }
print(alphabet[index])
print(index)
}
or enumerating the string indices:
func string_bits(userString: String) -> String {
var myString = ""
for (offset,index) in userString.indices.enumerated() {
if offset.isMultiple(of: 2) {
myString.append(userString[index])
}
}
return myString
}
ruby has the function string.squeeze, but I can't seem to find a swift equivalent.
For example I want to turn bookkeeper -> bokepr
Is my only option to create a set of the characters and then pull the characters from the set back to a string?
Is there a better way to do this?
Edit/update: Swift 4.2 or later
You can use a set to filter your duplicated characters:
let str = "bookkeeper"
var set = Set<Character>()
let squeezed = str.filter{ set.insert($0).inserted }
print(squeezed) // "bokepr"
Or as an extension on RangeReplaceableCollection which will also extend String and Substrings as well:
extension RangeReplaceableCollection where Element: Hashable {
var squeezed: Self {
var set = Set<Element>()
return filter{ set.insert($0).inserted }
}
}
let str = "bookkeeper"
print(str.squeezed) // "bokepr"
print(str[...].squeezed) // "bokepr"
I would use this piece of code from another answer of mine, which removes all duplicates of a sequence (keeping only the first occurrence of each), while maintaining order.
extension Sequence where Iterator.Element: Hashable {
func unique() -> [Iterator.Element] {
var alreadyAdded = Set<Iterator.Element>()
return self.filter { alreadyAdded.insert($0).inserted }
}
}
I would then wrap it with some logic which turns a String into a sequence (by getting its characters), unqiue's it, and then restores that result back into a string:
extension String {
func uniqueCharacters() -> String {
return String(self.characters.unique())
}
}
print("bookkeeper".uniqueCharacters()) // => "bokepr"
Here is a solution I found online, however I don't think it is optimal.
func removeDuplicateLetters(_ s: String) -> String {
if s.characters.count == 0 {
return ""
}
let aNum = Int("a".unicodeScalars.filter{$0.isASCII}.map{$0.value}.first!)
let characters = Array(s.lowercased().characters)
var counts = [Int](repeatElement(0, count: 26))
var visited = [Bool](repeatElement(false, count: 26))
var stack = [Character]()
var i = 0
for character in characters {
if let num = asciiValueOfCharacter(character) {
counts[num - aNum] += 1
}
}
for character in characters {
if let num = asciiValueOfCharacter(character) {
i = num - aNum
counts[i] -= 1
if visited[i] {
continue
}
while !stack.isEmpty, let peekNum = asciiValueOfCharacter(stack.last!), num < peekNum && counts[peekNum - aNum] != 0 {
visited[peekNum - aNum] = false
stack.removeLast()
}
stack.append(character)
visited[i] = true
}
}
return String(stack)
}
func asciiValueOfCharacter(_ character: Character) -> Int? {
let value = String(character).unicodeScalars.filter{$0.isASCII}.first?.value ?? 0
return Int(value)
}
Here is one way to do this using reduce(),
let newChar = str.characters.reduce("") { partial, char in
guard let _ = partial.range(of: String(char)) else {
return partial.appending(String(char))
}
return partial
}
As suggested by Leo, here is a bit shorter version of the same approach,
let newChar = str.characters.reduce("") { $0.range(of: String($1)) == nil ? $0.appending(String($1)) : $0 }
Just Another solution
let str = "Bookeeper"
let newChar = str.reduce("" , {
if $0.contains($1) {
return "\($0)"
} else {
return "\($0)\($1)"
}
})
print(str.replacingOccurrences(of: " ", with: ""))
Use filter and contains to remove duplicate values
let str = "bookkeeper"
let result = str.filter{!result.contains($0)}
print(result) //bokepr
What I want is something like
"word1 word2 word3".rangeOfWord(2) => 6 to 10
The result could come as a Range or a tuple or whatever.
I'd rather not do the brute force of iterating over the characters and using a state machine. Why reinvent the lexer? Is there a better way?
In your example, your words are unique, and you can use the following method:
let myString = "word1 word2 word3"
let wordNum = 2
let myRange = myString.rangeOfString(myString.componentsSeparatedByString(" ")[wordNum-1])
// 6..<11
As pointed out by Andrew Duncan in the comments below, the above is only valid if your words are unique. If you have non-unique words, you can use this somewhat less neater method:
let myString = "word1 word2 word3 word2 word1 word3 word1"
let wordNum = 7 // 2nd instance (out of 3) of "word1"
let arr = myString.componentsSeparatedByString(" ")
var fromIndex = arr[0..<wordNum-1].map { $0.characters.count }.reduce(0, combine: +) + wordNum - 1
let myRange = Range<String.Index>(start: myString.startIndex.advancedBy(fromIndex), end: myString.startIndex.advancedBy(fromIndex+arr[wordNum-1].characters.count))
let myWord = myString.substringWithRange(myRange)
// string "word1" (from range 36..<41)
Finally, lets use the latter to construct an extension of String as you have wished for in your question example:
extension String {
private func rangeOfNthWord(wordNum: Int, wordSeparator: String) -> Range<String.Index>? {
let arr = myString.componentsSeparatedByString(wordSeparator)
if arr.count < wordNum {
return nil
}
else {
let fromIndex = arr[0..<wordNum-1].map { $0.characters.count }.reduce(0, combine: +) + (wordNum - 1)*wordSeparator.characters.count
return Range<String.Index>(start: myString.startIndex.advancedBy(fromIndex), end: myString.startIndex.advancedBy(fromIndex+arr[wordNum-1].characters.count))
}
}
}
let myString = "word1 word2 word3 word2 word1 word3 word1"
let wordNum = 7 // 2nd instance (out of 3) of "word1"
if let myRange = myString.rangeOfNthWord(wordNum, wordSeparator: " ") {
// myRange: 36..<41
print(myString.substringWithRange(myRange)) // prints "word1"
}
You can tweak the .rangeOfNthWord(...) method if word separation is not unique (say some words are separated by two blankspaces " ").
Also pointed out in the comments below, the use of .rangeOfString(...) is not, per se, pure Swift. It is, however, by no means bad practice. From Swift Language Guide - Strings and Characters:
Swift’s String type is bridged with Foundation’s NSString class. If
you are working with the Foundation framework in Cocoa, the entire
NSString API is available to call on any String value you create when
type cast to NSString, as described in AnyObject. You can also use a
String value with any API that requires an NSString instance.
See also the NSString class reference for rangeOfString method:
// Swift Declaration:
func rangeOfString(_ searchString: String) -> NSRange
I went ahead and wrote the state machine. (Grumble..) FWIW, here it is:
extension String {
private func halfOpenIntervalOfBlock(n:Int, separator sep:Character? = nil) -> (Int, Int)? {
enum State {
case InSeparator
case InPrecedingSeparator
case InWord
case InTarget
case Done
}
guard n > 0 else {
return nil
}
var state:State
if n == 1 {
state = .InPrecedingSeparator
} else {
state = .InSeparator
}
var separatorNum = 0
var startIndex:Int = 0
var endIndex:Int = 0
for (i, c) in self.characters.enumerate() {
let inSeparator:Bool
// A bit inefficient to keep doing this test.
if let s = sep {
inSeparator = c == s
} else {
inSeparator = c == " " || c == "\n"
}
endIndex = i
switch state {
case .InPrecedingSeparator:
if !inSeparator {
state = .InTarget
startIndex = i
}
case .InTarget:
if inSeparator {
state = .Done
}
case .InWord:
if inSeparator {
separatorNum += 1
if separatorNum == n - 1 {
state = .InPrecedingSeparator
} else {
state = .InSeparator
}
}
case .InSeparator:
if !inSeparator {
state = .InWord
}
case .Done:
break
}
if state == .Done {
break
}
}
if state == .Done {
return (startIndex, endIndex)
} else if state == .InTarget {
return (startIndex, endIndex + 1) // We ran off end.
} else {
return nil
}
}
func rangeOfWord(n:Int) -> Range<Index>? {
guard let (s, e) = self.halfOpenIntervalOfBlock(n) else {
return nil
}
let ss = self.startIndex.advancedBy(s)
let ee = self.startIndex.advancedBy(e)
return Range(start:ss, end:ee)
}
}
It's not really clear whether the string has to be considered divided in words by separators it may contains, or if you're just looking for a specific substring occurrence.
Anyway both cases could be addressed in this way in my opinion:
extension String {
func enumerateOccurencies(of pattern: String, _ body: (Range<String.Index>, inout Bool) throws -> Void) rethrows {
guard
!pattern.isEmpty,
count >= pattern.count
else { return }
var stop = false
var lo = startIndex
while !stop && lo < endIndex {
guard
let r = self[lo..<endIndex].range(of: pattern)
else { break }
try body(r, &stop)
lo = r.upperBound
}
}
}
You'll then set stop to true in the body closure once reached the desired occurrence number and capture the range passed to it:
let words = "word1, word1, word2, word3, word1, word3"
var matches = 0
var rangeOfThirdOccurencyOfWord1: Range<String.Index>? = nil
words.enumerateOccurencies(of: "word1") { range, stop in
matches +=1
stop = matches == 3
if stop {
rangeOfThirdOccurencyOfWord1 = range
}
}
Regarding the DFA: recently I've wrote one leveraging on Hashable and using a an Array of Dictionaries as its state nodes, but I've found that the method above is faster, cause maybe range(of:) uses finger-printing.
UPDATE
Otherwise you could also achieve that API you've mentioned in this way:
import Foundation
extension String {
func rangeOfWord(order: Int, separator: String) -> Range<String.Index>? {
precondition(order > 0)
guard
!isEmpty,
!separator.isEmpty,
separator.count < count
else { return nil }
var wordsSoFar = 0
var lo = startIndex
while let r = self[lo..<endIndex].range(of: separator) {
guard
r.lowerBound != lo
else {
lo = r.upperBound
continue
}
wordsSoFar += 1
guard
wordsSoFar < order
else { return lo..<r.lowerBound }
lo = r.upperBound
}
if
lo < endIndex,
wordsSoFar + 1 == order
{
return lo..<endIndex
}
return nil
}
}
let words = "word anotherWord oneMore lastOne"
if let r = words.rangeOfWord(order: 4, separator: " ") {
print(words[r])
} else {
print("not found")
}
Here order parameter refers to the nth order of the word in the string, starting from 1. I've also added the separator parameter to specify a string token to use for finding words in the string (it can also be defaulted to " " to be able to call the function without having to specify it).
Here's my attempt at an updated answer in Swift 5.5:
import Foundation
extension String {
func rangeOfWord(atPosition wordAt: Int) -> Range<String.Index>? {
let fullrange = self.startIndex..<self.endIndex
var count = 0
var foundAt: Range<String.Index>? = nil
self.enumerateSubstrings(in: fullrange, options: .byWords) { _, substringRange, _, stop in
count += 1
if count == wordAt {
foundAt = substringRange
stop = true // Stop the enumeration after the word range is found.
}
}
return foundAt
}
}
let lorem = "Morbi leo risus, porta ac consectetur ac, vestibulum at eros."
if let found = lorem.rangeOfWord(atPosition: 8) {
print("found: \(lorem[found])")
} else {
print("not found.")
}
This solution doesn't make a new array to contain the words so uses less memory (I have not tested but in theory it should use less memory). As much as possible, the build in method is used therefore less chance of bugs.
Swift 5 solution, which allows you to specify the word separator
extension String {
func rangeOfWord(atIndex wordIndex: Int) -> Range<String.Index>? {
let wordComponents = self.components(separatedBy: " ")
guard wordIndex < wordComponents.count else {
return nil
}
let characterEndCount = wordComponents[0...wordIndex].map { $0.count }.reduce(0, +)
let start = String.Index(utf16Offset: wordIndex + characterEndCount - wordComponents[wordIndex].count, in: self)
let end = String.Index(utf16Offset: wordIndex + characterEndCount, in: self)
return start..<end
}
}
I like many of the features in Swift, but using manipulating strings are still a big pain in the ass.
func checkPalindrome(word: String) -> Bool {
print(word)
if word == "" {
return true
} else {
if word.characters.first == word.characters.last {
return checkPalindrome(word.substringWithRange(word.startIndex.successor() ..< word.endIndex.predecessor()))
} else {
return false
}
}
}
This code fails miserably whenever the string's length is an odd number. Of course I could make it so the first line of the block would be if word.characters.count < 2, but is there a way in Swift to get substrings and check easily?
Update
I like many of the suggestions, but I guess the original question could be misleading a little, since it's a question about String more than getting the right results for the function.
For instance, in Python, checkPalindrome(word[1:-1]) would work fine for the recursive definition, whereas Swift code is much less graceful since it needs other bells and whistles.
return word == String(word.reversed())
func isPalindrome(myString:String) -> Bool {
let reverseString = String(myString.characters.reversed())
if(myString != "" && myString == reverseString) {
return true
} else {
return false
}
}
print(isPalindrome("madam"))
I have used the below extension to find whether the number is Palindrome or Not.
extension String {
var isPalindrome: Bool {
return self == String(self.reversed())
}
}
Sometimes having a front end for a recursion can simplify life. I sometimes do this when the arguments which are most convenient to use are not what I want in the user interface.
Would the following meet your needs?
func checkPalindrome(str: String) -> Bool {
func recursiveTest(var charSet: String.CharacterView) -> Bool {
if charSet.count < 2 {
return true
} else {
if charSet.popFirst() != charSet.popLast() {
return false
} else {
return recursiveTest(charSet)
}
}
}
return recursiveTest(str.characters)
}
just add on more condition in if
func checkPalindrome(word: String) -> Bool {
print(word)
if (word == "" || word.characters.count == 1){
return true
}
else {
if word.characters.first == word.characters.last {
return checkPalindrome(word.substringWithRange(word.startIndex.successor() ..< word.endIndex.predecessor()))
} else {
return false
}
}
}
extension StringProtocol where Self: RangeReplaceableCollection {
var letters: Self { filter(\.isLetter) }
var isPalindrome: Bool {
let letters = self.letters
return String(letters.reversed()).caseInsensitiveCompare(letters) == .orderedSame
}
}
"Dammit I'm Mad".isPalindrome // true
"Socorram-me subi no onibus em marrocos".isPalindrome // true
You can also break your string into an array of characters and iterate through them until its half comparing one by one with its counterpart:
func checkPalindrome(_ word: String) -> Bool {
let chars = Array(word.letters.lowercased())
for index in 0..<chars.count/2 {
if chars[index] != chars[chars.count - 1 - index] {
return false
}
}
return true
}
And the recursive version fixing the range issue where can't form a range with endIndex < startIndex:
func checkPalindrome<T: StringProtocol>(_ word: T) -> Bool {
let word = word.lowercased()
.components(separatedBy: .punctuationCharacters).joined()
.components(separatedBy: .whitespacesAndNewlines).joined()
if word == "" || word.count == 1 {
return true
} else {
if word.first == word.last {
let start = word.index(word.startIndex,offsetBy: 1, limitedBy: word.endIndex) ?? word.startIndex
let end = word.index(word.endIndex,offsetBy: -1, limitedBy: word.startIndex) ?? word.endIndex
return checkPalindrome(word[start..<end])
} else {
return false
}
}
}
checkPalindrome("Dammit I'm Mad")
I think if you make an extension to String like this one then it will make your life easier:
extension String {
var length: Int { return characters.count }
subscript(index: Int) -> Character {
return self[startIndex.advancedBy(index)]
}
subscript(range: Range<Int>) -> String {
return self[Range<Index>(start: startIndex.advancedBy(range.startIndex), end: startIndex.advancedBy(range.endIndex))]
}
}
With it in place, you can change your function to this:
func checkPalindrome(word: String) -> Bool {
if word.length < 2 {
return true
}
if word.characters.first != word.characters.last {
return false
}
return checkPalindrome(word[1..<word.length - 1])
}
Quick test:
print(checkPalindrome("aba")) // Prints "true"
print(checkPalindrome("abc")) // Prints "false"
extension String {
func trimmingFirstAndLastCharacters() -> String {
guard let startIndex = index(self.startIndex, offsetBy: 1, limitedBy: self.endIndex) else {
return self
}
guard let endIndex = index(self.endIndex, offsetBy: -1, limitedBy: self.startIndex) else {
return self
}
guard endIndex >= startIndex else {
return self
}
return String(self[startIndex..<endIndex])
}
var isPalindrome: Bool {
guard count > 1 else {
return true
}
return first == last && trimmingFirstAndLastCharacters().isPalindrome
}
}
We first declare a function that removes first and last characters from a string.
Next we declare a computer property which will contain the actual recursive code that checks if a string is palindrome.
If string's size is less than or equal 1 we immediately return true (strings composed by one character like "a" or the empty string "" are considered palindrome), otherwise we check if first and last characters of the string are the same and we recursively call isPalindrome on the current string deprived of the first and last characters.
Convert the string into an Array. When the loop is executed get the first index and compare with the last index.
func palindrome(string: String)-> Bool{
let char = Array(string)
for i in 0..<char.count / 2 {
if char[i] != char[char.count - 1 - i] {
return false
}
}
return true
}
This solution is not recursive, but it is a O(n) pure index based solution without filtering anything and without creating new objects. Non-letter characters are ignored as well.
It uses two indexes and walks outside in from both sides.
I admit that the extension type and property name is stolen from Leo, I apologize. 😉
extension StringProtocol where Self: RangeReplaceableCollection {
var isPalindrome : Bool {
if isEmpty { return false }
if index(after: startIndex) == endIndex { return true }
var forward = startIndex
var backward = endIndex
while forward < backward {
repeat { formIndex(before: &backward) } while !self[backward].isLetter
if self[forward].lowercased() != self[backward].lowercased() { return false }
repeat { formIndex(after: &forward) } while !self[forward].isLetter
}
return true
}
}
Wasn't really thinking of this, but I think I came up with a pretty cool extension, and thought I'd share.
extension String {
var subString: (Int?) -> (Int?) -> String {
return { (start) in
{ (end) in
let startIndex = start ?? 0 < 0 ? self.endIndex.advancedBy(start!) : self.startIndex.advancedBy(start ?? 0)
let endIndex = end ?? self.characters.count < 0 ? self.endIndex.advancedBy(end!) : self.startIndex.advancedBy(end ?? self.characters.count)
return startIndex > endIndex ? "" : self.substringWithRange(startIndex ..< endIndex)
}
}
}
}
let test = ["Eye", "Pop", "Noon", "Level", "Radar", "Kayak", "Rotator", "Redivider", "Detartrated", "Tattarrattat", "Aibohphobia", "Eve", "Bob", "Otto", "Anna", "Hannah", "Evil olive", "Mirror rim", "Stack cats", "Doom mood", "Rise to vote sir", "Step on no pets", "Never odd or even", "A nut for a jar of tuna", "No lemon, no melon", "Some men interpret nine memos", "Gateman sees name, garageman sees nametag"]
func checkPalindrome(word: String) -> Bool {
if word.isEmpty { return true }
else {
if word.subString(nil)(1) == word.subString(-1)(nil) {
return checkPalindrome(word.subString(1)(-1))
} else {
return false
}
}
}
for item in test.map({ $0.lowercaseString.stringByReplacingOccurrencesOfString(",", withString: "").stringByReplacingOccurrencesOfString(" ", withString: "") }) {
if !checkPalindrome(item) {
print(item)
}
}
A simple solution in Swift:
func isPalindrome(word: String) -> Bool {
// If no string found, return false
if word.count == 0 { return false }
var index = 0
var characters = Array(word) // make array of characters
while index < characters.count / 2 { // repeat loop only for half length of given string
if characters[index] != characters[(characters.count - 1) - index] {
return false
}
index += 1
}
return true
}
func checkPalindrome(_ inputString: String) -> Bool {
if inputString.count % 2 == 0 {
return false
} else if inputString.count == 1 {
return true
} else {
var stringCount = inputString.count
while stringCount != 1 {
if inputString.first == inputString.last {
stringCount -= 2
} else {
continue
}
}
if stringCount == 1 {
return true
} else {
return false
}
}
}
I have an array ["abc", "94761178","790"]
I want to iterate each and check is a String or an Int?
How to check it?
How to convert "123" to integer 123?
Here is a small Swift version using String extension :
Swift 3/Swift 4 :
extension String {
var isNumber: Bool {
return !isEmpty && rangeOfCharacter(from: CharacterSet.decimalDigits.inverted) == nil
}
}
Swift 2 :
extension String {
var isNumber : Bool {
get{
return !self.isEmpty && self.rangeOfCharacterFromSet(NSCharacterSet.decimalDigitCharacterSet().invertedSet) == nil
}
}
}
Edit Swift 2.2:
In swift 2.2 use Int(yourArray[1])
var yourArray = ["abc", "94761178","790"]
var num = Int(yourArray[1])
if num != nil {
println("Valid Integer")
}
else {
println("Not Valid Integer")
}
It will show you that string is valid integer and num contains valid Int.You can do your calculation with num.
From docs:
If the string represents an integer that fits into an Int, returns the
corresponding integer.This accepts strings that match the regular
expression "[-+]?[0-9]+" only.
Be aware that checking a string/number using the Int initializer has limits. Specifically, a max value of 2^32-1 or 4294967295. This can lead to problems, as a phone number of 8005551234 will fail the Int(8005551234) check despite being a valid number.
A much safer approach is to use NSCharacterSet to check for any characters matching the decimal set in the range of the string.
let number = "8005551234"
let numberCharacters = NSCharacterSet.decimalDigitCharacterSet().invertedSet
if !number.isEmpty && number.rangeOfCharacterFromSet(numberCharacters) == nil {
// string is a valid number
} else {
// string contained non-digit characters
}
Additionally, it could be useful to add this to a String extension.
public extension String {
func isNumber() -> Bool {
let numberCharacters = NSCharacterSet.decimalDigitCharacterSet().invertedSet
return !self.isEmpty && self.rangeOfCharacterFromSet(numberCharacters) == nil
}
}
I think the nicest solution is:
extension String {
var isNumeric : Bool {
return Double(self) != nil
}
}
Starting from Swift 2, String.toInt() was removed.
A new Int Initializer was being introduced: Int(str: String)
for target in ["abc", "94761178","790"]
{
if let number = Int(target)
{
print("value: \(target) is a valid number. add one to get :\(number+1)!")
}
else
{
print("value: \(target) is not a valid number.")
}
}
Swift 3, 4
extension String {
var isNumber: Bool {
let characters = CharacterSet.decimalDigits.inverted
return !self.isEmpty && rangeOfCharacter(from: characters) == nil
}
}
Simple solution like this:
extension String {
public var isNumber: Bool {
return !isEmpty && rangeOfCharacter(from: CharacterSet.decimalDigits.inverted) == nil
}
}
I think using NumberFormatter is an easy way:
(Swift 5)
import Foundation
extension String {
private static let numberFormatter = NumberFormatter()
var isNumeric : Bool {
Self.numberFormatter.number(from: self) != nil
}
}
The correct way is to use the toInt() method of String, and an optional binding to determine whether the conversion succeeded or not. So your loop would look like:
let myArray = ["abc", "94761178","790"]
for val in myArray {
if let intValue = val.toInt() {
// It's an int
println(intValue)
} else {
// It's not an int
println(val)
}
}
The toInt() method returns an Int?, so an optional Int, which is nil if the string cannot be converted ton an integer, or an Int value (wrapped in the optional) if the conversion succeeds.
The method documentation (shown using CMD+click on toInt in Xcode) says:
If the string represents an integer that fits into an Int, returns the corresponding integer. This accepts strings that match the regular expression "[-+]?[0-9]+" only.
This way works also with strings with mixed numbers:
public extension String {
func isNumber() -> Bool {
return !self.isEmpty && self.rangeOfCharacter(from: CharacterSet.decimalDigits) != nil && self.rangeOfCharacter(from: CharacterSet.letters) == nil
}}
So u get something like this:
Swift 3.0 version
func isNumber(stringToTest : String) -> Bool {
let numberCharacters = CharacterSet.decimalDigits.inverted
return !s.isEmpty && s.rangeOfCharacter(from:numberCharacters) == nil
}
If you want to accept a more fine-grained approach (i.e. accept a number like 4.5 or 3e10), you proceed like this:
func isNumber(val: String) -> Bool
{
var result: Bool = false
let parseDotComNumberCharacterSet = NSMutableCharacterSet.decimalDigitCharacterSet()
parseDotComNumberCharacterSet.formUnionWithCharacterSet(NSCharacterSet(charactersInString: ".e"))
let noNumberCharacters = parseDotComNumberCharacterSet.invertedSet
if let v = val
{
result = !v.isEmpty && v.rangeOfCharacterFromSet(noNumberCharacters) == nil
}
return result
}
For even better resolution, you might draw on regular expression..
Xcode 8 and Swift 3.0
We can also check :
//MARK: - NUMERIC DIGITS
class func isString10Digits(ten_digits: String) -> Bool{
if !ten_digits.isEmpty {
let numberCharacters = NSCharacterSet.decimalDigits.inverted
return !ten_digits.isEmpty && ten_digits.rangeOfCharacter(from: numberCharacters) == nil
}
return false
}
This code works for me for Swift 3/4
func isNumber(textField: UITextField) -> Bool {
let allowedCharacters = CharacterSet.decimalDigits
let characterSet = CharacterSet(charactersIn: textField.text!)
return allowedCharacters.isSuperset(of: characterSet)
// return true
}
You can use this for integers of any length.
func getIntegerStrings(from givenStrings: [String]) -> [String]
{
var integerStrings = [String]()
for string in givenStrings
{
let isValidInteger = isInteger(givenString: string)
if isValidInteger { integerStrings.append(string) }
}
return integerStrings
}
func isInteger(givenString: String) -> Bool
{
var answer = true
givenString.forEach { answer = ("0"..."9").contains($0) && answer }
return answer
}
func getIntegers(from integerStrings: [String]) -> [Int]
{
let integers = integerStrings.compactMap { Int($0) }
return integers
}
let strings = ["abc", "94761178", "790", "18446744073709551615000000"]
let integerStrings = getIntegerStrings(from: strings)
let integers = getIntegers(from: integerStrings)
print(integerStrings) // ["94761178", "790", "18446744073709551615000000"]
print(integers) // [94761178, 790]
However, as pointed out by #Can, you can get the integer value for the number only up to 2^31 - 1 (signed integer limit on 32-bit arch). For the larger value, however, you will still get the string representation.
This code will return an array of converted integers:
["abc", "94761178","790"].map(Int.init) // returns [ nil, 94761178, 790 ]
OR
["abc", "94761178","790"].map { Int($0) ?? 0 } // returns [ 0, 94761178, 790 ]
Get the following isInteger() function from the below stackoverflow post posted by corsiKa:
Determine if a String is an Integer in Java
And I think this is what you want to do (where nameOfArray is the array you want to pass)
void convertStrArrayToIntArray( int[] integerArray ) {
for (int i = 0; i < nameOfArray.length(); i++) {
if (!isInteger(nameOfArray[i])) {
integerArray[i] = nameOfArray[i].toString();
}
}
}