Strip Non-Alphanumeric Characters from an NSString - cocoa

Question

I'm looking for a quick and easy way to strip non-alphanumeric characters from an NSString. Probably something using an NSCharacterSet, but I'm tired and nothing seems to return a string containing only the alphanumeric characters in a string.

Answer 1

We can do this by splitting and then joining. Requires OS X 10.5+ for the componentsSeparatedByCharactersInSet:
NSCharacterSet *charactersToRemove = [[NSCharacterSet alphanumericCharacterSet] invertedSet];
NSString *strippedReplacement = [[someString componentsSeparatedByCharactersInSet:charactersToRemove] componentsJoinedByString:#""];

Answer 2

In Swift, the componentsJoinedByString is replaced by join(...), so here it just replaces non-alphanumeric characters with a space.
let charactersToRemove = NSCharacterSet.alphanumericCharacterSet().invertedSet
let strippedReplacement = " ".join(someString.componentsSeparatedByCharactersInSet(charactersToRemove))
For Swift2 ...
var enteredByUser = field.text .. or whatever
let unsafeChars = NSCharacterSet.alphanumericCharacterSet().invertedSet
enteredByUser = enteredByUser
.componentsSeparatedByCharactersInSet(unsafeChars)
.joinWithSeparator("")
If you want to delete just the one character, for example delete all returns...
enteredByUser = enteredByUser
.componentsSeparatedByString("\n")
.joinWithSeparator("")

Answer 3

What I wound up doing was creating an NSCharacterSet and the -invertedSet method that I found (it's a wonder what an extra hour of sleep does for documentation-reading abilities). Here's the code snippet, assuming that someString is the string from which you want to remove non-alphanumeric characters:
NSCharacterSet *charactersToRemove =
[[ NSCharacterSet alphanumericCharacterSet ] invertedSet ];
NSString *trimmedReplacement =
[ someString stringByTrimmingCharactersInSet:charactersToRemove ];
trimmedReplacement will then contain someString's alphanumeric characters.

Answer 4

Swift 3 version of accepted answer:
let unsafeChars = CharacterSet.alphanumerics.inverted
let myStrippedString = myString.components(separatedBy: unsafeChars).joined(separator: "")

Answer 5

Swift 5, Extension:
extension String {
/// Will strip all non alpha characters from a string
public var alpha: String {
return components(separatedBy: CharacterSet.alphanumerics.inverted).joined()
}
}

Answer 6

A Cleanup Category
I have a method call stringByStrippingCharactersInSet: and stringByCollapsingWhitespace that might be convenient to just drop-in.
#implementation NSString (Cleanup)
- (NSString *)clp_stringByStrippingCharactersInSet:(NSCharacterSet *)set
{
return [[self componentsSeparatedByCharactersInSet:set] componentsJoinedByString:#""];
}
- (NSString *)clp_stringByCollapsingWhitespace
{
NSArray *components = [self componentsSeparatedByCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
components = [components filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:#"self <> ''"]];
return [components componentsJoinedByString:#" "];
}
#end

Answer 7

Here’s a Swift version of Cameron’s category as an extension:
extension String {
func stringByStrippingCharactersInSet(set:NSCharacterSet) -> String
{
return (self.componentsSeparatedByCharactersInSet(set) as NSArray).componentsJoinedByString("")
}
func stringByCollapsingWhitespace() -> String
{
var components:NSArray = self.componentsSeparatedByCharactersInSet(NSCharacterSet.whitespaceCharacterSet())
let predicate = NSPredicate(format: "self <> ''", argumentArray: nil)
components = components.filteredArrayUsingPredicate(predicate)
return components.componentsJoinedByString(" ")
}
}

Answer 8

The plain cycle would be the faster execution time I think:
#implementation NSString(MyUtil)
- (NSString*) stripNonNumbers {
NSMutableString* res = [NSMutableString new];
//NSCharacterSet *numericSet = [NSCharacterSet decimalDigitCharacterSet];
for ( int i=0; i < self.length; ++i ) {
unichar c = [self characterAtIndex:i];
if ( c >= '0' && c <= '9' ) // this looks cleaner, but a bit slower: [numericSet characterIsMember:c])
[res appendFormat:#"%c", c];
}
return res;
}
#end

Answer 9

This is a more effective way than the provided answer
+ (NSString *)alphanumericString:(NSString *)s {
NSCharacterSet * charactersToRemove = [[NSCharacterSet alphanumericCharacterSet] invertedSet];
NSMutableString * ms = [NSMutableString stringWithCapacity:[s length]];
for (NSInteger i = 0; i < s.length; ++i) {
unichar c = [s characterAtIndex:i];
if (![charactersToRemove characterIsMember:c]) {
[ms appendFormat:#"%c", c];
}
}
return ms;
}
or as a Category
#implementation NSString (Alphanumeric)
- (NSString *)alphanumericString {
NSCharacterSet * charactersToRemove = [[NSCharacterSet alphanumericCharacterSet] invertedSet];
NSMutableString * ms = [NSMutableString stringWithCapacity:[self length]];
for (NSInteger i = 0; i < self.length; ++i) {
unichar c = [self characterAtIndex:i];
if (![charactersToRemove characterIsMember:c]) {
[ms appendFormat:#"%c", c];
}
}
return ms;
}
#end