So I got stuck on a coding challenge that I almost knew the answer too. And I think I have to use the subString call in Swift 4 to get it 100%. I want to reverse every OTHER word in a string, but ignore or keep the punctuation in its original place( index ).
var sample = "lets start. And not worry about proper sentences."
func reverseString(inputString: String) -> String {
let oldSentence = sample.components(separatedBy: " ")
var newSentence = ""
for index in 0...oldSentence.count - 1 {
let word = oldSentence[index]
if newSentence != "" {
newSentence += " "
}
if index % 2 == 1 {
let reverseWord = String(word.reversed())
newSentence += reverseWord
} else {
newSentence += word
}
}
return newSentence
}
reverseString(inputString: sample)
And this would be the expected output.
"lets trats. And ton worry tuoba proper secnetnes."
Notice the punctuation is not reversed.
You shouldn't use components(separatedBy: ) to split a string in words. See this article for the reason. Use enumerateSubstrings and pass in the appropriate option:
func reverseString(inputString: String) -> String {
var index = 1
var newSentence = inputString
inputString.enumerateSubstrings(in: inputString.startIndex..., options: .byWords) { substr, range, _, stop in
guard let substr = substr else { return }
if index % 2 == 0 {
newSentence = newSentence.replacingCharacters(in: range, with: String(substr.reversed()))
}
index += 1
}
return newSentence
}
print(reverseString(inputString: "lets start. And not worry about proper sentences."))
// lets trats. And ton worry tuoba proper secnetnes.
print(reverseString(inputString: "I think, therefore I'm"))
// I kniht, therefore m'I
I am trying to add attributes to some ranges in Swift String.
I found ranges of first and last symbol in substring and color the text between them (including) in red.
let mutableString = NSMutableAttributedString(string: text)
let str = mutableString.string
//Red symbols
var t = 0
let symbols = mutableString.string.characters.count
while t < symbols {
if str[t] == "[" {
let startIndex = t
while str[t] != "]" {
t += 1
}
t += 1
let endIndex = t
mutableString.addAttribute(
NSForegroundColorAttributeName,
value: UIColor.redColor(),
range: NSMakeRange(startIndex, endIndex - startIndex))
}
t += 1
}
But I found that ranges in String and in NSMutableAttributedString are not equal. Range in String is shorter (this text is not in Unicode encoding).
Is there a some way to find ranges not in underlying String but in NSAttributedString to find it correctly?
Example:
print(mutableString.length) //550
print(mutableString.string.characters.count) //548
Why is this difference?
Yes it is possible to find ranges in NSMutableAttributedString.
Example :
let text = "[I love Ukraine!]"
var start = text.rangeOfString("[")
var finish = text.rangeOfString("]")
let mutableString = NSMutableAttributedString(string: text)
let startIndex = mutableString.string.rangeOfString("[")
let finishIndex = mutableString.string.rangeOfString("]")
Example output from playground:
Distinguish between String and NSString, even though they are bridged to one another. String is native Swift, and you define a range in terms of String character index. NSString is Cocoa (Foundation), and you define a range in terms of NSRange.
Yes, I found it.
Windows end-of-line "\r\n" is two symbols in NSAttributedString but only one character in Swift String.
I use checking in my code:
let symbols = mutableString.string.characters.count
var extendedSymbols = 0
while t < symbols {
if str[t] == "\r\n" { extendedSymbols += 1 }
else if str[t] == "[" {
let startIndex = t + extendedSymbols
while str[t] != "]" {
t += 1
}
t += 1
let endIndex = t + extendedSymbols
mutableString.addAttribute(
NSForegroundColorAttributeName,
value: UIColor.redColor(),
range: NSMakeRange(startIndex, endIndex - startIndex))
}
t += 1
}
Thank you all for help!!!
How could I replace nth character of a String with another one?
func replace(myString:String, index:Int, newCharac:Character) -> String {
// Write correct code here
return modifiedString
}
For example, replace("House", 2, "r") should be equal to "Horse".
Solutions that use NSString methods will fail for any strings with multi-byte Unicode characters. Here are two Swift-native ways to approach the problem:
You can use the fact that a String is a sequence of Character to convert the string to an array, modify it, and convert the array back:
func replace(myString: String, _ index: Int, _ newChar: Character) -> String {
var chars = Array(myString) // gets an array of characters
chars[index] = newChar
let modifiedString = String(chars)
return modifiedString
}
replace("House", 2, "r")
// Horse
Alternately, you can step through the string yourself:
func replace(myString: String, _ index: Int, _ newChar: Character) -> String {
var modifiedString = String()
for (i, char) in myString.characters.enumerate() {
modifiedString += String((i == index) ? newChar : char)
}
return modifiedString
}
Since these stay entirely within Swift, they're both Unicode-safe:
replace("🏠🏡🏠🏡🏠", 2, "🐴")
// 🏠🏡🐴🏡🏠
In Swift 4 it's much easier.
let newString = oldString.prefix(n) + char + oldString.dropFirst(n + 1)
This is an example:
let oldString = "Hello, playground"
let newString = oldString.prefix(4) + "0" + oldString.dropFirst(5)
where the result is
Hell0, playground
The type of newString is Substring. Both prefix and dropFirst return Substring. Substring is a slice of a string, in other words, substrings are fast because you don't need to allocate memory for the content of the string, but the same storage space as the original string is used.
I've found this solution.
var string = "Cars"
let index = string.index(string.startIndex, offsetBy: 2)
string.replaceSubrange(index...index, with: "t")
print(string)
// Cats
Please see NateCook answer for more details
func replace(myString: String, _ index: Int, _ newChar: Character) -> String {
var chars = Array(myString.characters) // gets an array of characters
chars[index] = newChar
let modifiedString = String(chars)
return modifiedString
}
For Swift 5
func replace(myString: String, _ index: Int, _ newChar: Character) -> String {
var chars = Array(myString) // gets an array of characters
chars[index] = newChar
let modifiedString = String(chars)
return modifiedString
}
replace("House", 2, "r")
This is no longer valid and deprecated.
You can always use swift String with NSString.So you can call NSString function on swift String.
By old stringByReplacingCharactersInRange: you can do like this
var st :String = "House"
let abc = st.bridgeToObjectiveC().stringByReplacingCharactersInRange(NSMakeRange(2,1), withString:"r") //Will give Horse
For modify existing string:
extension String {
subscript(_ n: Int) -> Character {
get {
let idx = self.index(startIndex, offsetBy: n)
return self[idx]
}
set {
let idx = self.index(startIndex, offsetBy: n)
self.replaceSubrange(idx...idx, with: [newValue])
}
}
}
var s = "12345"
print(s[0])
s[0] = "9"
print(s)
I've expanded upon Nate Cooks answer and transformed it into a string extension.
extension String {
//Enables replacement of the character at a specified position within a string
func replace(_ index: Int, _ newChar: Character) -> String {
var chars = Array(characters)
chars[index] = newChar
let modifiedString = String(chars)
return modifiedString
}
}
usage:
let source = "House"
let result = source.replace(2,"r")
result is "Horse"
I think what #Greg was trying to achieve with his extension is this:
mutating func replace(characterAt index: Int, with newChar: Character) {
var chars = Array(characters)
if index >= 0 && index < self.characters.count {
chars[index] = newChar
let modifiedString = String(chars)
self = modifiedString
} else {
print("can't replace character, its' index out of range!")
}
}
usage:
let source = "House"
source.replace(characterAt: 2, with: "r") //gives you "Horse"
After looking at the Swift Docs, I managed to make this function:
//Main function
func replace(myString:String, index:Int, newCharac:Character) -> String {
//Looping through the characters in myString
var i = 0
for character in myString {
//Checking to see if the index of the character is the one we're looking for
if i == index {
//Found it! Now instead of adding it, add newCharac!
modifiedString += newCharac
} else {
modifiedString += character
}
i = i + 1
}
// Write correct code here
return modifiedString
}
Please note that this is untested, but it should give you the right idea.
func replace(myString:String, index:Int, newCharac:Character) -> String {
var modifiedString = myString
let range = Range<String.Index>(
start: advance(myString.startIndex, index),
end: advance(myString.startIndex, index + 1))
modifiedString.replaceRange(range, with: "\(newCharac)")
return modifiedString
}
I would prefer to pass a String than a Character though.
Here's a way to replace a single character:
var string = "This is the original string."
let offset = 27
let index = string.index(string.startIndex, offsetBy: offset)
let range = index...index
print("ORIGINAL string: " + string)
string.replaceSubrange(range, with: "!")
print("UPDATED string: " + string)
// ORIGINAL string: This is the original string.
// UPDATED string: This is the original string!
This works with multi-character strings as well:
var string = "This is the original string."
let offset = 7
let index = string.index(string.startIndex, offsetBy: offset)
let range = index...index
print("ORIGINAL string: " + string)
string.replaceSubrange(range, with: " NOT ")
print("UPDATED string: " + string)
// ORIGINAL string: This is the original string.
// UPDATED string: This is NOT the original string.
var s = "helloworld"
let index = ((s.count) / 2) // index is 4
let firstIndex = s.index(s.startIndex, offsetBy: index)
let secondIndex = s.index(s.startIndex, offsetBy: index)
s.replaceSubrange(firstIndex...secondIndex, with: "*")
print("Replaced string is: \(s)") //OUTPUT IS: hell*world
This is working fine to replace string using the index.
String class in Swift (till v5 and maybe later) is what other languages call a StringBuilder class, and for performance reasons, Swift does NOT provide setting character by index; If you don't care about performance a simple solution could be:
public static func replace(_ string: String, at index: Int, with value: String) {
let start = string.index(string.startIndex, offsetBy: index)
let end = string.index(start, offsetBy: 1)
string.replaceSubrange(start..<end, with: value)
}
Or as an extension:
extension String {
public func charAt(_ index: Int) -> Character {
return self[self.index(self.startIndex, offsetBy: index)];
}
public mutating func setCharAt(_ index: Int, _ new: Character) {
self.setCharAt(index, String(new))
}
public mutating func setCharAt(_ index: Int, _ new: String) {
let i = self.index(self.startIndex, offsetBy: index)
self.replaceSubrange(i...i, with: new)
}
}
Note how above needs to call index(...) method to convert integer to actual-index!? It seems, Swift implements String like a linked-list, where append(...) is really fast, but even finding the index (without doing anything with it) is a linear-time operation (and gets slower based on concatenation count).
public void createEncodedSentence() {
StringBuffer buff = new StringBuffer();
int counter = 0;
char a;
for (int i = 0; i < sentence.length(); i++) {
a = sentence.charAt(i);
if (a == '.') {
buff.append('*');
}
if (a != ' ' && a != '.') {
counter++;
}
if (counter % 3 == 0) {
buff.append("");
}
buff.append(sentence.charAt(i));
}
encodedSentence = buff.toString();
}
Strings in swift don't have an accessor to read or write a single character. There's an excellent blog post by Ole Begemann describing how strings in swift work.
Note: the implementation below is wrong, read addendum
So the right way is by taking the left part of the string up to the index -1 character, append the replacing character, then append the string from index + 1 up to the end:
func myReplace(myString:String, index:Int, newCharac:Character) -> String {
var modifiedString: String
let len = countElements(myString)
if (index < len) && (index >= 0) {
modifiedString = myString.substringToIndex(index) + newCharac + myString.substringFromIndex(index + 1)
} else {
modifiedString = myString
}
return modifiedString
}
Note: in my implementation I chose to return the original string if the index is not in a valid range
Addendum Thanks to #slazyk, who found out that my implementation is wrong (see comment), I am providing a new swift only version of the function.
func replace(myString:String, index:Int, newCharac:Character) -> String {
var modifiedString: String
if (index < 0) || (index >= countElements(myString)) {
modifiedString = myString
} else {
var start = myString.startIndex
var end = advance(start, index)
modifiedString = myString[start ..< end]
modifiedString += newCharac
start = end.successor()
end = myString.endIndex
modifiedString += myString[start ... end]
}
return modifiedString
}
#codester's answer looks very good, and it's probably what I would use myself.
It would be interesting to know how performances compare though, using a fully swift solution and bridging to objective-c instead.
Here is an efficient answer :
import Foundation
func replace(myString:String, index:Int, newCharac:Character) -> String {
return myString.substringToIndex(index-1) + newCharac + myString.substringFromIndex(index)
}
I made a console program, but the problem is that it doesn't allow parameters to be inserted. So I'm wondering how would I split a single string into multiple strings to achieve what I need. E.g.: text="msg Hello" would be split into textA="msg" and textB="Hello"
This is the main console code so far (just to show the idea):
if (keyboard_check_pressed(vk_enter)) {
text_console_c = asset_get_index("scr_local_"+string(keyboard_string));
if (text_console_c > -1) {
text_console+= "> "+keyboard_string+"#";
script_execute(text_console_c);
text_console_c = -1;
}
else if (keyboard_string = "") {
text_console+= ">#";
}
else {
text_console+= "> Unknown command: "+keyboard_string+"#";
};
keyboard_string = "";
}
I cant recommend spliting string with iteration by char, because when u try split very very very long string, then time to split is very long and can freeze thread for a short/long time. Game maker is single threaded for now.
This code is much faster.
string_split
var str = argument[0] //string to split
var delimiter = argument[1] // delimiter
var letDelimiter = false // append delimiter to each part
if(argument_count == 3)
letDelimiter = argument[2]
var list = ds_list_create()
var d_at = string_pos(delimiter, str)
while(d_at > 0) {
var part = string_delete(str, d_at , string_length(str))
if(letDelimiter)
part = part + delimiter
str = string_delete(str, 1, d_at)
d_at = string_pos(delimiter, str)
ds_list_add(list, part)
if(d_at == 0 && str != "")//last string without delimiter, need to add too
ds_list_add(list, str)
}
return list;
Dont forget ds_list_destroy after you iterate all strings
for example:
var splited = string_split("first part|second part", '|')
for(splited) {
//do something with each string
}
ds_list_destroy(splited)
Something like this may help, haven't tested it out but if you can follow what is going on its a good place to start.
Text = "msg Hello"
counter = 0
stringIndex = 0
for (i = 0; i < string_length(text); i++)
{
if string_char_at(text,i) == " "
{
counter++
stringIndex = 0
} else {
string_insert(string_char_at(text,i),allStrings(counter),stringIndex)
stringIndex++
}
}
allStrings should be an array containing each of the separate strings. Whenever a " " is seen the next index of allStrings starts having it's characters filled in. stringIndex is used to add the progressive characters.
Given a string text which contains newline there is a search keyword which matches an item within the text.
How do I implement the following in C#:
searchIdx = search index (starting with 0, then 1, etc. for each successive call to GetSearchContext. Initially start with 0.
contextsTxt = string data to search in
searchTxt = keyword to search for in contextsTxt
numLines = number of lines to return surrounding the searchTxt found (ie. 1 = the line the searchTxt is found on, 2 = the line the searchTxt is found on, 3 = the line above the searchTxt is found on, the line the searchTxt is found on, and the line below the searchTxt is found on)
returns the "context" based on the parameters
string GetSearchContext(int searchIdx, string contentsTxt, string searchTxt, int numLines);
If there's a better function interface to accomplish this feel free to suggest that as well.
I tried the following but doesn't seem to work properly all the time:
private string GetSearchContext(string contentValue, string search, int numLines)
{
int searchIdx = contentValue.IndexOf(search);
int startIdx = 0;
int lastIdx = 0;
while (startIdx != -1 && (startIdx = contentValue.IndexOf('\n', startIdx+1)) < searchIdx)
{
lastIdx = startIdx;
}
startIdx = lastIdx;
if (startIdx < 0)
startIdx = 0;
int endIdx = searchIdx;
int lineCnt = 0;
while (endIdx != -1 && lineCnt++ < numLines)
{
endIdx = contentValue.IndexOf('\n', endIdx + 1);
}
if (endIdx == -1 || endIdx > contentValue.Length - 1)
endIdx = contentValue.Length - 1;
string lines = contentValue.Substring(startIdx, endIdx - startIdx + 1);
if (lines[0] == '\n')
lines = lines.Substring(1);
if (lines[lines.Length - 1] == '\n')
{
lines = lines.Substring(0, lines.Length - 1);
}
if (lines[lines.Length - 1] == '\r')
{
lines = lines.Substring(0, lines.Length - 1);
}
return lines;
}
it's not actually a homework question. i'm trying to build a personal search engine. I just now figured out the problem as to why it didn't always work which was due to case-sensitive searching.
Just needed to add StringComparison.CurrentCultureIgnoreCase and voila it worked! I feel dumb for not thinking of that before posting.