Replace multiple characters in a string in Objective-C? - iphone

Question

In PHP I can do this:
$new = str_replace(array('/', ':', '.'), '', $new);
...to replace all instances of the characters / : . with a blank string (to remove them)
Can I do this easily in Objective-C? Or do I have to roll my own?
Currently I am doing multiple calls to stringByReplacingOccurrencesOfString:
strNew = [strNew stringByReplacingOccurrencesOfString:#"/" withString:#""];
strNew = [strNew stringByReplacingOccurrencesOfString:#":" withString:#""];
strNew = [strNew stringByReplacingOccurrencesOfString:#"." withString:#""];
Thanks,
matt

Answer 1

A somewhat inefficient way of doing this:
NSString *s = #"foo/bar:baz.foo";
NSCharacterSet *doNotWant = [NSCharacterSet characterSetWithCharactersInString:#"/:."];
s = [[s componentsSeparatedByCharactersInSet: doNotWant] componentsJoinedByString: #""];
NSLog(#"%#", s); // => foobarbazfoo
Look at NSScanner and -[NSString rangeOfCharacterFromSet: ...] if you want to do this a bit more efficiently.

Answer 2

There are situations where your method is good enough I think matt.. BTW, I think it's better to use
[strNew setString: [strNew stringByReplacingOccurrencesOfString:#":" withString:#""]];
rather than
strNew = [strNew stringByReplacingOccurrencesOfString:#"/" withString:#""];
as I think you're overwriting an NSMutableString pointer with an NSString which might cause a memory leak.

Answer 3

Had to do this recently and wanted to share an efficient method:
(assuming someText is a NSString or text attribute)
NSString* someText = #"1232342jfahadfskdasfkjvas12!";
(this example will strip numbers from a string)
[someText stringByReplacingOccurrencesOfString:#"[^0-9]" withString:#"" options:NSRegularExpressionSearch range:NSMakeRange(0, [someText length])];
Keep in mind that you will need to escape regex literal characters using Obj-c escape character:
(obj-c uses a double backslash to escape special regex literals)
...stringByReplacingOccurrencesOfString:#"[\\\!\\.:\\/]"
What makes this interesting is that NSRegularExpressionSearch option is little used but can lead to some very powerful controls:
You can find a nice iOS regex tutorial here and more on regular expressions at regex101.com

Answer 4

Essentially the same thing as Nicholas posted above, but if you want to remove everything EXCEPT a set of characters (say you want to remove everything that isn't in the set "ABCabc123") then you can do the following:
NSString *s = #"A567B$%C^.123456abcdefg";
NSCharacterSet *doNotWant = [[NSCharacterSet characterSetWithCharactersInString:#"ABCabc123"] invertedSet];
s = [[s componentsSeparatedByCharactersInSet: doNotWant] componentsJoinedByString: #""];
NSLog(#"%#", s); // => ABC123abc
Useful in stripping out symbols and such, if you only want alphanumeric.

Answer 5

+ (NSString*) decodeHtmlUnicodeCharactersToString:(NSString*)str
{
NSMutableString* string = [[NSMutableString alloc] initWithString:str]; // #&39; replace with '
NSString* unicodeStr = nil;
NSString* replaceStr = nil;
int counter = -1;
for(int i = 0; i < [string length]; ++i)
{
unichar char1 = [string characterAtIndex:i];
for (int k = i + 1; k < [string length] - 1; ++k)
{
unichar char2 = [string characterAtIndex:k];
if (char1 == '&' && char2 == '#' )
{
++counter;
unicodeStr = [string substringWithRange:NSMakeRange(i + 2 , 2)]; // read integer value i.e, 39
replaceStr = [string substringWithRange:NSMakeRange (i, 5)]; // #&39;
[string replaceCharactersInRange: [string rangeOfString:replaceStr] withString:[NSString stringWithFormat:#"%c",[unicodeStr intValue]]];
break;
}
}
}
[string autorelease];
if (counter > 1)
return [self decodeHtmlUnicodeCharactersToString:string];
else
return string;
}

Answer 6

Here is an example in Swift 3 using the regularExpression option of replacingOccurances.
Use replacingOccurrences along with a the String.CompareOptions.regularExpression option.
Example (Swift 3):
var x = "<Hello, [play^ground+]>"
let y = x.replacingOccurrences(of: "[\\[\\]^+<>]", with: "7", options: .regularExpression, range: nil)
print(y)
Output:
7Hello, 7play7ground777

Answer 7

If the characters you wish to remove were to be adjacent to each other you could use the
stringByReplacingCharactersInRange:(NSRange) withString:(NSString *)
Other than that, I think just using the same function several times isn't that bad. It is much more readable than creating a big method to do the same in a more generic way.

Answer 8

Create an extension on String...
extension String {
func replacingOccurrences(of strings:[String], with replacement:String) -> String {
var newString = self
for string in strings {
newString = newString.replacingOccurrences(of: string, with: replacement)
}
return newString
}
}
Call it like this:
aString = aString.replacingOccurrences(of:['/', ':', '.'], with:"")