Testing in Playground I read a whole file in an array of String, one string per line.
But what I need is a specific line only:
let dir = try? FileManager.default.url(for: .documentDirectory,
in: .userDomainMask, appropriateFor: nil, create: true)
let fileURL = dir!.appendingPathComponent("test").appendingPathExtension("txt")
let text: [String] = try String(contentsOf: fileURL).components(separatedBy: NSCharacterSet.newlines)
let i = 2 // computed before, here to simplify
print(text[i])
There is a way to avoid reading the complete big file?
I'm guessing you mean that you want to retrieve the index without manually searching the array with, say, a for-in loop.
In Swift 4 you can use Array.index(where:) in combination with the StringProtocol's generic contains(_:) function to find what you're looking for.
Let's imagine you're looking for the first line containing the text "important stuff" in your text: [String] array.
You could use:
text.index(where: { $0.contains("important stuff") })
Behind the scenes, Swift is looping to find the text, but with built-in enhancements, this should perform better than manually looping through the text array.
Note that the result of this search could be nil if no matching lines are present. Therefore, you'll need to ensure it's not nil before using the result:
Force unwrap the result (risking the dreaded fatal error: unexpectedly found nil while unwrapping an Optional value):
print(text[lineIndex!)
Or, use an if let statement:
if let lineIndex = stringArray.index(where: { $0.contains("important stuff") }) {
print(text[lineIndex])
}
else {
print("Sorry; didn't find any 'important stuff' in the array.")
}
Or, use a guard statement:
guard let lineIndex = text.index(where: {$0.contains("important stuff")}) else {
print("Sorry; didn't find any 'important stuff' in the array.")
return
}
print(text[lineIndex])
To find a specific line without reading the entire file in, you could use this StreamReader answer. It contains code that worked in Swift 3. I tested it in Swift 4, as well: see my GitHub repo, TEST-StreamReader, for my test code.
You would still have to loop to get to the right line, but then break the loop once you've retrieved that line.
Here's the StreamReader class from that SO answer:
class StreamReader {
let encoding : String.Encoding
let chunkSize : Int
var fileHandle : FileHandle!
let delimData : Data
var buffer : Data
var atEof : Bool
init?(path: String, delimiter: String = "\n", encoding: String.Encoding = .utf8,
chunkSize: Int = 4096) {
guard let fileHandle = FileHandle(forReadingAtPath: path),
let delimData = delimiter.data(using: encoding) else {
return nil
}
self.encoding = encoding
self.chunkSize = chunkSize
self.fileHandle = fileHandle
self.delimData = delimData
self.buffer = Data(capacity: chunkSize)
self.atEof = false
}
deinit {
self.close()
}
/// Return next line, or nil on EOF.
func nextLine() -> String? {
precondition(fileHandle != nil, "Attempt to read from closed file")
// Read data chunks from file until a line delimiter is found:
while !atEof {
if let range = buffer.range(of: delimData) {
// Convert complete line (excluding the delimiter) to a string:
let line = String(data: buffer.subdata(in: 0..<range.lowerBound), encoding: encoding)
// Remove line (and the delimiter) from the buffer:
buffer.removeSubrange(0..<range.upperBound)
return line
}
let tmpData = fileHandle.readData(ofLength: chunkSize)
if tmpData.count > 0 {
buffer.append(tmpData)
} else {
// EOF or read error.
atEof = true
if buffer.count > 0 {
// Buffer contains last line in file (not terminated by delimiter).
let line = String(data: buffer as Data, encoding: encoding)
buffer.count = 0
return line
}
}
}
return nil
}
/// Start reading from the beginning of file.
func rewind() -> Void {
fileHandle.seek(toFileOffset: 0)
buffer.count = 0
atEof = false
}
/// Close the underlying file. No reading must be done after calling this method.
func close() -> Void {
fileHandle?.closeFile()
fileHandle = nil
}
}
extension StreamReader : Sequence {
func makeIterator() -> AnyIterator<String> {
return AnyIterator {
return self.nextLine()
}
}
}
I've been working with the code form this answer, provided by Martin R. The code is awesome and it is very useful. However, it doesn't work with the links, while working fine with files. After putting some NSLogs and breaks, I have actually found that problem is in this code block:
init?(path: String, delimiter: String = "\n", encoding: UInt = NSUTF8StringEncoding, chunkSize : Int = 4096) {
self.chunkSize = chunkSize
self.encoding = encoding
self.fileHandle = NSFileHandle(forReadingFromURL: NSURL(string: path)!, error: nil)
println("PATH IS \(path)")
println("FILE HANDLE IS \(fileHandle)")
if self.fileHandle == nil {
println("FILE HANDLE IS NIL!")
return nil
}
The code above actually contains some minor changes, compared with Martin's answer. Also Apple says that it is possible to use fileHandle with forReadingFromURL and it shouldn't return nil.
But here is the console output:
PATH IS http://smth.com
FILE HANDLE IS nil
FILE HANDLE IS NIL!!!!!
The question is what's wrong?
UPDATE
As Martin R has kindly explained to me, this code won't work with URLs, this answer states the same, so I have rewritten the code, guiding by previous answers:
import Foundation
import Cocoa
class StreamReader {
let encoding : UInt
let chunkSize : Int
var atEof : Bool = false
var streamData : NSData!
var fileLength : Int
var urlRequest : NSMutableURLRequest
var currentOffset : Int
var streamResponse : NSString
var fileHandle : NSFileHandle!
let buffer : NSMutableData!
let delimData : NSData!
var reponseError: NSError?
var response: NSURLResponse?
init?(path: NSURL, delimiter: String = "\n", encoding: UInt = NSUTF8StringEncoding, chunkSize : Int = 10001000) {
println("YOUR PATH IS \(path)")
self.chunkSize = chunkSize
self.encoding = encoding
self.currentOffset = 0
urlRequest = NSMutableURLRequest(URL: path)
streamData = NSURLConnection.sendSynchronousRequest(urlRequest, returningResponse:&response, error:&reponseError)
streamResponse = NSString(data:streamData!, encoding:NSUTF8StringEncoding)!
self.fileLength = streamData.length
//println("WHAT IS STREAMDATA \(streamData)")
//println("WHAT IS URLREQUEST \(urlRequest)")
if streamData == nil {
println("LINK HAS NO CONTENT!!!!!")
}
self.fileLength = streamResponse.length
println("FILE LENGTH IS \(fileLength)")
self.buffer = NSMutableData(capacity: chunkSize)!
// Create NSData object containing the line delimiter:
delimData = delimiter.dataUsingEncoding(NSUTF8StringEncoding)!
println("WHAT DOES THE DELIMITER \(delimiter)LOOK LIKE?")
println("WHAT IS DELIMDATA \(delimData)")
}
deinit {
self.close()
}
/// Return next line, or nil on EOF.
func nextLine() -> String? {
if atEof {
println("AT THE END OF YOUR FILE!!!")
return nil
}
// Read data chunks from file until a line delimiter is found:
if currentOffset >= fileLength {
return nil
}
var blockLength : Int = buffer.length
var range = buffer.rangeOfData(delimData, options: NSDataSearchOptions(0), range: NSMakeRange(currentOffset, blockLength))
//println("STREAM DATA \(streamData)")
println("RANGE IS \(range)")
while range.location == NSNotFound {
var nRange = NSMakeRange(currentOffset, chunkSize)
println("nRange is \(nRange)")
var tmpData = streamData.subdataWithRange(nRange)
//println("TMP data length \(tmpData.length)")
currentOffset += blockLength
//println("TMPDATA is \(tmpData)")
if tmpData.length == 0 {
// EOF or read error.
println("ERROR ????")
atEof = true
if buffer.length > 0 {
// Buffer contains last line in file (not terminated by delimiter).
let line = NSString(data: buffer, encoding: encoding);
buffer.length = 0
println("THE LINE IS \(line)")
return line
}
// No more lines.
return nil
}
buffer.appendData(tmpData)
range = buffer.rangeOfData(delimData, options: NSDataSearchOptions(0), range: NSMakeRange(0, buffer.length))
}
// Convert complete line (excluding the delimiter) to a string:
let line = NSString(data: buffer.subdataWithRange(NSMakeRange(0, range.location)),
encoding: encoding)
// Remove line (and the delimiter) from the buffer:
buffer.replaceBytesInRange(NSMakeRange(0, range.location + range.length), withBytes: nil, length: 0)
return line
}
/// Start reading from the beginning of file.
func rewind() -> Void {
//streamData.seekToFileOffset(0)
buffer.length = 0
atEof = false
}
/// Close the underlying file. No reading must be done after calling this method.
func close() -> Void {
if streamData != nil {
streamData = nil
}
}
}
extension StreamReader : SequenceType {
func generate() -> GeneratorOf<String> {
return GeneratorOf<String> {
return self.nextLine()
}
}
}
But actually this code is very far from being perfect and I would like to see any recommendations on improving it. Please, be kind. I am very amateur and very inexperienced( but sooner or later I will learn it)
Finally, it is working. And probably the last problem is left, the code doesn't stop, it continues to read file from the beginning.
So now the question is probably more close to 'What's wrong with my code?', compared with previous: 'What's wrong?'
UPDATE
I have rewritten last parts of code like this:
let line = NSString(data: buffer.subdataWithRange(NSMakeRange(0, range.location + 1)),
encoding: encoding)
buffer.replaceBytesInRange(NSMakeRange(0, range.location + range.length), withBytes: nil, length: 0)
println("COMPLETE LINE IS \(line)")
if line!.containsString("\n"){
println("CONTAINS NEW LINE")
//println("BUFFER IS \(buffer)")
//
println("COMPLETE LINE IS \(line)")
return line
}
else {
println("NO LINE!")
atEof == true
return nil
}
The idea is to go through all the lines which contain \n and to exclude one line, which is the last one and shouldn't have the \n. But! Despite the fact that I have checked non-printing characters and there was no \n, here is the surprising console output: Optional("lastline_blablabla\n")
Probably now the question is, how to stop at the last line even if it contains \n?
If you need to retrieve data from the URL my code above (the one under first update) will work
But my own problem with \n has several ways to be solved. One of which I used in my code. As it's very individual I won't post the solution to \n at the end of file issue. Also I am not sure that my both solutions for urlStreamReader and \n are the best, so if you advice any better solution it will be much appreciated by me and probably some other people.
Great thanks to Martin R, who explained a lot, wrote great code and was very nice
I have not yet been able to figure out how to get a substring of a String in Swift:
var str = “Hello, playground”
func test(str: String) -> String {
return str.substringWithRange( /* What goes here? */ )
}
test (str)
I'm not able to create a Range in Swift. Autocomplete in the Playground isn’t super helpful - this is what it suggests:
return str.substringWithRange(aRange: Range<String.Index>)
I haven't found anything in the Swift Standard Reference Library that helps. Here was another wild guess:
return str.substringWithRange(Range(0, 1))
And this:
let r:Range<String.Index> = Range<String.Index>(start: 0, end: 2)
return str.substringWithRange(r)
I've seen other answers (Finding index of character in Swift String) that seem to suggest that since String is a bridge type for NSString, the "old" methods should work, but it's not clear how - e.g., this doesn't work either (doesn't appear to be valid syntax):
let x = str.substringWithRange(NSMakeRange(0, 3))
Thoughts?
You can use the substringWithRange method. It takes a start and end String.Index.
var str = "Hello, playground"
str.substringWithRange(Range<String.Index>(start: str.startIndex, end: str.endIndex)) //"Hello, playground"
To change the start and end index, use advancedBy(n).
var str = "Hello, playground"
str.substringWithRange(Range<String.Index>(start: str.startIndex.advancedBy(2), end: str.endIndex.advancedBy(-1))) //"llo, playgroun"
You can also still use the NSString method with NSRange, but you have to make sure you are using an NSString like this:
let myNSString = str as NSString
myNSString.substringWithRange(NSRange(location: 0, length: 3))
Note: as JanX2 mentioned, this second method is not safe with unicode strings.
Swift 2
Simple
let str = "My String"
let subStr = str[str.startIndex.advancedBy(3)...str.startIndex.advancedBy(7)]
//"Strin"
Swift 3
let startIndex = str.index(str.startIndex, offsetBy: 3)
let endIndex = str.index(str.startIndex, offsetBy: 7)
str[startIndex...endIndex] // "Strin"
str.substring(to: startIndex) // "My "
str.substring(from: startIndex) // "String"
Swift 4
substring(to:) and substring(from:) are deprecated in Swift 4.
String(str[..<startIndex]) // "My "
String(str[startIndex...]) // "String"
String(str[startIndex...endIndex]) // "Strin"
At the time I'm writing, no extension is perfectly Swift 4.2 compatible, so here is one that covers all the needs I could think of:
extension String {
func substring(from: Int?, to: Int?) -> String {
if let start = from {
guard start < self.count else {
return ""
}
}
if let end = to {
guard end >= 0 else {
return ""
}
}
if let start = from, let end = to {
guard end - start >= 0 else {
return ""
}
}
let startIndex: String.Index
if let start = from, start >= 0 {
startIndex = self.index(self.startIndex, offsetBy: start)
} else {
startIndex = self.startIndex
}
let endIndex: String.Index
if let end = to, end >= 0, end < self.count {
endIndex = self.index(self.startIndex, offsetBy: end + 1)
} else {
endIndex = self.endIndex
}
return String(self[startIndex ..< endIndex])
}
func substring(from: Int) -> String {
return self.substring(from: from, to: nil)
}
func substring(to: Int) -> String {
return self.substring(from: nil, to: to)
}
func substring(from: Int?, length: Int) -> String {
guard length > 0 else {
return ""
}
let end: Int
if let start = from, start > 0 {
end = start + length - 1
} else {
end = length - 1
}
return self.substring(from: from, to: end)
}
func substring(length: Int, to: Int?) -> String {
guard let end = to, end > 0, length > 0 else {
return ""
}
let start: Int
if let end = to, end - length > 0 {
start = end - length + 1
} else {
start = 0
}
return self.substring(from: start, to: to)
}
}
And then, you can use:
let string = "Hello,World!"
string.substring(from: 1, to: 7)gets you: ello,Wo
string.substring(to: 7)gets you: Hello,Wo
string.substring(from: 3)gets you: lo,World!
string.substring(from: 1, length: 4)gets you: ello
string.substring(length: 4, to: 7)gets you: o,Wo
Updated substring(from: Int?, length: Int) to support starting from zero.
NOTE: #airspeedswift makes some very insightful points on the trade-offs of this approach, particularly the hidden performance impacts. Strings are not simple beasts, and getting to a particular index may take O(n) time, which means a loop that uses a subscript can be O(n^2). You have been warned.
You just need to add a new subscript function that takes a range and uses advancedBy() to walk to where you want:
import Foundation
extension String {
subscript (r: Range<Int>) -> String {
get {
let startIndex = self.startIndex.advancedBy(r.startIndex)
let endIndex = startIndex.advancedBy(r.endIndex - r.startIndex)
return self[Range(start: startIndex, end: endIndex)]
}
}
}
var s = "Hello, playground"
println(s[0...5]) // ==> "Hello,"
println(s[0..<5]) // ==> "Hello"
(This should definitely be part of the language. Please dupe rdar://17158813)
For fun, you can also add a + operator onto the indexes:
func +<T: ForwardIndex>(var index: T, var count: Int) -> T {
for (; count > 0; --count) {
index = index.succ()
}
return index
}
s.substringWithRange(s.startIndex+2 .. s.startIndex+5)
(I don't know yet if this one should be part of the language or not.)
SWIFT 2.0
simple:
let myString = "full text container"
let substring = myString[myString.startIndex..<myString.startIndex.advancedBy(3)] // prints: ful
SWIFT 3.0
let substring = myString[myString.startIndex..<myString.index(myString.startIndex, offsetBy: 3)] // prints: ful
SWIFT 4.0
Substring operations return an instance of the Substring type, instead of String.
let substring = myString[myString.startIndex..<myString.index(myString.startIndex, offsetBy: 3)] // prints: ful
// Convert the result to a String for long-term storage.
let newString = String(substring)
It is much more simple than any of the answers here, once you find the right syntax.
I want to take away the [ and ]
let myString = "[ABCDEFGHI]"
let startIndex = advance(myString.startIndex, 1) //advance as much as you like
let endIndex = advance(myString.endIndex, -1)
let range = startIndex..<endIndex
let myNewString = myString.substringWithRange( range )
result will be "ABCDEFGHI"
the startIndex and endIndex could also be used in
let mySubString = myString.substringFromIndex(startIndex)
and so on!
PS: As indicated in the remarks, there are some syntax changes in swift 2 which comes with xcode 7 and iOS9!
Please look at this page
For example to find the first name (up to the first space) in my full name:
let name = "Joris Kluivers"
let start = name.startIndex
let end = find(name, " ")
if end {
let firstName = name[start..end!]
} else {
// no space found
}
start and end are of type String.Index here and are used to create a Range<String.Index> and used in the subscript accessor (if a space is found at all in the original string).
It's hard to create a String.Index directly from an integer position as used in the opening post. This is because in my name each character would be of equal size in bytes. But characters using special accents in other languages could have used several more bytes (depending on the encoding used). So what byte should the integer refer to?
It's possible to create a new String.Index from an existing one using the methods succ and pred which will make sure the correct number of bytes are skipped to get to the next code point in the encoding. However in this case it's easier to search for the index of the first space in the string to find the end index.
Since String is a bridge type for NSString, the "old" methods should work, but it's not clear how - e.g., this doesn't work either (doesn't appear to be valid syntax):
let x = str.substringWithRange(NSMakeRange(0, 3))
To me, that is the really interesting part of your question. String is bridged to NSString, so most NSString methods do work directly on a String. You can use them freely and without thinking. So, for example, this works just as you expect:
// delete all spaces from Swift String stateName
stateName = stateName.stringByReplacingOccurrencesOfString(" ", withString:"")
But, as so often happens, "I got my mojo workin' but it just don't work on you." You just happened to pick one of the rare cases where a parallel identically named Swift method exists, and in a case like that, the Swift method overshadows the Objective-C method. Thus, when you say str.substringWithRange, Swift thinks you mean the Swift method rather than the NSString method — and then you are hosed, because the Swift method expects a Range<String.Index>, and you don't know how to make one of those.
The easy way out is to stop Swift from overshadowing like this, by casting explicitly:
let x = (str as NSString).substringWithRange(NSMakeRange(0, 3))
Note that no significant extra work is involved here. "Cast" does not mean "convert"; the String is effectively an NSString. We are just telling Swift how to look at this variable for purposes of this one line of code.
The really weird part of this whole thing is that the Swift method, which causes all this trouble, is undocumented. I have no idea where it is defined; it is not in the NSString header and it's not in the Swift header either.
The short answer is that this is really hard in Swift right now. My hunch is that there is still a bunch of work for Apple to do on convenience methods for things like this.
String.substringWithRange() is expecting a Range<String.Index> parameter, and as far as I can tell there isn't a generator method for the String.Index type. You can get String.Index values back from aString.startIndex and aString.endIndex and call .succ() or .pred() on them, but that's madness.
How about an extension on the String class that takes good old Ints?
extension String {
subscript (r: Range<Int>) -> String {
get {
let subStart = advance(self.startIndex, r.startIndex, self.endIndex)
let subEnd = advance(subStart, r.endIndex - r.startIndex, self.endIndex)
return self.substringWithRange(Range(start: subStart, end: subEnd))
}
}
func substring(from: Int) -> String {
let end = countElements(self)
return self[from..<end]
}
func substring(from: Int, length: Int) -> String {
let end = from + length
return self[from..<end]
}
}
let mobyDick = "Call me Ishmael."
println(mobyDick[8...14]) // Ishmael
let dogString = "This 🐶's name is Patch."
println(dogString[5..<6]) // 🐶
println(dogString[5...5]) // 🐶
println(dogString.substring(5)) // 🐶's name is Patch.
println(dogString.substring(5, length: 1)) // 🐶
Update: Swift beta 4 resolves the issues below!
As it stands [in beta 3 and earlier], even Swift-native strings have some issues with handling Unicode characters. The dog icon above worked, but the following doesn't:
let harderString = "1:1️⃣"
for character in harderString {
println(character)
}
Output:
1
:
1
️
⃣
In new Xcode 7.0 use
//: Playground - noun: a place where people can play
import UIKit
var name = "How do you use String.substringWithRange?"
let range = name.startIndex.advancedBy(0)..<name.startIndex.advancedBy(10)
name.substringWithRange(range)
//OUT:
You can use this extensions to improve substringWithRange
Swift 2.3
extension String
{
func substringWithRange(start: Int, end: Int) -> String
{
if (start < 0 || start > self.characters.count)
{
print("start index \(start) out of bounds")
return ""
}
else if end < 0 || end > self.characters.count
{
print("end index \(end) out of bounds")
return ""
}
let range = Range(start: self.startIndex.advancedBy(start), end: self.startIndex.advancedBy(end))
return self.substringWithRange(range)
}
func substringWithRange(start: Int, location: Int) -> String
{
if (start < 0 || start > self.characters.count)
{
print("start index \(start) out of bounds")
return ""
}
else if location < 0 || start + location > self.characters.count
{
print("end index \(start + location) out of bounds")
return ""
}
let range = Range(start: self.startIndex.advancedBy(start), end: self.startIndex.advancedBy(start + location))
return self.substringWithRange(range)
}
}
Swift 3
extension String
{
func substring(start: Int, end: Int) -> String
{
if (start < 0 || start > self.characters.count)
{
print("start index \(start) out of bounds")
return ""
}
else if end < 0 || end > self.characters.count
{
print("end index \(end) out of bounds")
return ""
}
let startIndex = self.characters.index(self.startIndex, offsetBy: start)
let endIndex = self.characters.index(self.startIndex, offsetBy: end)
let range = startIndex..<endIndex
return self.substring(with: range)
}
func substring(start: Int, location: Int) -> String
{
if (start < 0 || start > self.characters.count)
{
print("start index \(start) out of bounds")
return ""
}
else if location < 0 || start + location > self.characters.count
{
print("end index \(start + location) out of bounds")
return ""
}
let startIndex = self.characters.index(self.startIndex, offsetBy: start)
let endIndex = self.characters.index(self.startIndex, offsetBy: start + location)
let range = startIndex..<endIndex
return self.substring(with: range)
}
}
Usage:
let str = "Hello, playground"
let substring1 = str.substringWithRange(0, end: 5) //Hello
let substring2 = str.substringWithRange(7, location: 10) //playground
Sample Code for how to get substring in Swift 2.0
(i) Substring from starting index
Input:-
var str = "Swift is very powerful language!"
print(str)
str = str.substringToIndex(str.startIndex.advancedBy(5))
print(str)
Output:-
Swift is very powerful language!
Swift
(ii) Substring from particular index
Input:-
var str = "Swift is very powerful language!"
print(str)
str = str.substringFromIndex(str.startIndex.advancedBy(6)).substringToIndex(str.startIndex.advancedBy(2))
print(str)
Output:-
Swift is very powerful language!
is
I hope it will help you!
Easy solution with little code.
Make an extension that includes basic subStringing that nearly all other languages have:
extension String {
func subString(start: Int, end: Int) -> String {
let startIndex = self.index(self.startIndex, offsetBy: start)
let endIndex = self.index(startIndex, offsetBy: end)
let finalString = self.substring(from: startIndex)
return finalString.substring(to: endIndex)
}
}
Simply call this with
someString.subString(start: 0, end: 6)
This works in my playground :)
String(seq: Array(str)[2...4])
Updated for Xcode 7. Adds String extension:
Use:
var chuck: String = "Hello Chuck Norris"
chuck[6...11] // => Chuck
Implementation:
extension String {
/**
Subscript to allow for quick String substrings ["Hello"][0...1] = "He"
*/
subscript (r: Range<Int>) -> String {
get {
let start = self.startIndex.advancedBy(r.startIndex)
let end = self.startIndex.advancedBy(r.endIndex - 1)
return self.substringWithRange(start..<end)
}
}
}
try this in playground
var str:String = "Hello, playground"
let range = Range(start:advance(str.startIndex,1), end: advance(str.startIndex,8))
it will give you "ello, p"
However where this gets really interesting is that if you make the last index bigger than the string in playground it will show any strings that you defined after str :o
Range() appears to be a generic function so that it needs to know the type it is dealing with.
You also have to give it the actual string your interested in playgrounds as it seems to hold all stings in a sequence one after another with their variable name afterwards.
So
var str:String = "Hello, playground"
var str2:String = "I'm the next string"
let range = Range(start:advance(str.startIndex,1), end: advance(str.startIndex,49))
gives "ello, playground�str���I'm the next string�str2�"
works even if str2 is defined with a let
:)
Rob Napier had already given a awesome answer using subscript. But i felt one drawback in that as there is no check for out of bound conditions. This can tend to crash. So i modified the extension and here it is
extension String {
subscript (r: Range<Int>) -> String? { //Optional String as return value
get {
let stringCount = self.characters.count as Int
//Check for out of boundary condition
if (stringCount < r.endIndex) || (stringCount < r.startIndex){
return nil
}
let startIndex = self.startIndex.advancedBy(r.startIndex)
let endIndex = self.startIndex.advancedBy(r.endIndex - r.startIndex)
return self[Range(start: startIndex, end: endIndex)]
}
}
}
Output below
var str2 = "Hello, World"
var str3 = str2[0...5]
//Hello,
var str4 = str2[0..<5]
//Hello
var str5 = str2[0..<15]
//nil
So i suggest always to check for the if let
if let string = str[0...5]
{
//Manipulate your string safely
}
In Swift3
For ex: a variable "Duke James Thomas", we need to get "James".
let name = "Duke James Thomas"
let range: Range<String.Index> = name.range(of:"James")!
let lastrange: Range<String.Index> = img.range(of:"Thomas")!
var middlename = name[range.lowerBound..<lstrange.lowerBound]
print (middlename)
Taking a page from Rob Napier, I developed these Common String Extensions, two of which are:
subscript (r: Range<Int>) -> String
{
get {
let startIndex = advance(self.startIndex, r.startIndex)
let endIndex = advance(self.startIndex, r.endIndex - 1)
return self[Range(start: startIndex, end: endIndex)]
}
}
func subString(startIndex: Int, length: Int) -> String
{
var start = advance(self.startIndex, startIndex)
var end = advance(self.startIndex, startIndex + length)
return self.substringWithRange(Range<String.Index>(start: start, end: end))
}
Usage:
"Awesome"[3...7] //"some"
"Awesome".subString(3, length: 4) //"some"
This is how you get a range from a string:
var str = "Hello, playground"
let startIndex = advance(str.startIndex, 1)
let endIndex = advance(startIndex, 8)
let range = startIndex..<endIndex
let substr = str[range] //"ello, pl"
The key point is that you are passing a range of values of type String.Index (this is what advance returns) instead of integers.
The reason why this is necessary, is that strings in Swift don't have random access (because of variable length of Unicode characters basically). You also can't do str[1]. String.Index is designed to work with their internal structure.
You can create an extension with a subscript though, that does this for you, so you can just pass a range of integers (see e.g. Rob Napier's answer).
I tried to come up with something Pythonic.
All the subscripts here are great, but the times I really need something simple is usually when I want to count from back, e.g. string.endIndex.advancedBy(-1)
It supports nil values, for both start and end index, where nil would mean index at 0 for start, string.characters.count for end.
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 dog = "Dog‼🐶"
print(dog.subString(nil)(-1)) // Dog!!
EDIT
A more elegant solution:
public extension String {
struct Substring {
var start: Int?
var string: String
public subscript(end: Int?) -> String {
let startIndex = start ?? 0 < 0 ? string.endIndex.advancedBy(start!) : string.startIndex.advancedBy(start ?? 0)
let endIndex = end ?? string.characters.count < 0 ? string.endIndex.advancedBy(end!) : string.startIndex.advancedBy(end ?? string.characters.count)
return startIndex > endIndex ? "" : string.substringWithRange(startIndex ..< endIndex)
}
}
public subscript(start: Int?) -> Substring {
return Substring(start: start, string: self)
}
}
let dog = "Dog‼🐶"
print(dog[nil][-1]) // Dog!!
First create the range, then the substring. You can use fromIndex..<toIndex syntax like so:
let range = fullString.startIndex..<fullString.startIndex.advancedBy(15) // 15 first characters of the string
let substring = fullString.substringWithRange(range)
here is a example to get video-Id only .i.e (6oL687G0Iso) from the whole URL in swift
let str = "https://www.youtube.com/watch?v=6oL687G0Iso&list=PLKmzL8Ib1gsT-5LN3V2h2H14wyBZTyvVL&index=2"
var arrSaprate = str.componentsSeparatedByString("v=")
let start = arrSaprate[1]
let rangeOfID = Range(start: start.startIndex,end:start.startIndex.advancedBy(11))
let substring = start[rangeOfID]
print(substring)
let startIndex = text.startIndex
var range = startIndex.advancedBy(1) ..< text.endIndex.advancedBy(-4)
let substring = text.substringWithRange(range)
Full sample you can see here
http://www.learnswiftonline.com/reference-guides/string-reference-guide-for-swift/
shows that this works well:
var str = "abcd"
str = str.substringToIndex(1)
Well, I had the same issue and solved with the "bridgeToObjectiveC()" function:
var helloworld = "Hello World!"
var world = helloworld.bridgeToObjectiveC().substringWithRange(NSMakeRange(6,6))
println("\(world)") // should print World!
Please note that in the example, substringWithRange in conjunction with NSMakeRange take the part of the string starting at index 6 (character "W") and finishing at index 6 + 6 positions ahead (character "!")
Cheers.
You can use any of the substring methods in a Swift String extension I wrote https://bit.ly/JString.
var string = "hello"
var sub = string.substringFrom(3) // or string[3...5]
println(sub)// "lo"
If you have an NSRange, bridging to NSString works seamlessly. For example, I was doing some work with UITextFieldDelegate and I quickly wanted to compute the new string value when it asked if it should replace the range.
func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
let newString = (textField.text as NSString).stringByReplacingCharactersInRange(range, withString: string)
println("Got new string: ", newString)
}
Simple extension for String:
extension String {
func substringToIndex(index: Int) -> String {
return self[startIndex...startIndex.advancedBy(min(index, characters.count - 1))]
}
}
If you don't care about performance... this is probably the most concise solution in Swift 4
extension String {
subscript(range: CountableClosedRange<Int>) -> String {
return enumerated().filter{$0.offset >= range.first! && $0.offset < range.last!}
.reduce(""){$0 + String($1.element)}
}
}
It enables you to do something like this:
let myStr = "abcd"
myStr[0..<2] // produces "ab"