Call a method on every word in NSString - objective-c

Question

I would like to loop through an NSString and call a custom function on every word that has certain criterion (For example, "has 2 'L's"). I was wondering what the best way of approaching that was. Should I use Find/Replace patterns? Blocks?
-(NSString *)convert:(NSString *)wordToConvert{
/// This I have already written
Return finalWord;
}
-(NSString *) method:(NSString *) sentenceContainingWords{
// match every word that meets the criteria (for example the 2Ls) and replace it with what convert: does.
}

Answer 1

To enumerate the words in a string, you should use -[NSString enumerateSubstringsInRange:options:usingBlock:] with NSStringEnumerationByWords and NSStringEnumerationLocalized. All of the other methods listed use a means of identifying words which may not be locale-appropriate or correspond to the system definition. For example, two words separated by a comma but not whitespace (e.g. "foo,bar") would not be treated as separate words by any of the other answers, but they are in Cocoa text views.
[aString enumerateSubstringsInRange:NSMakeRange(0, [aString length])
options:NSStringEnumerationByWords | NSStringEnumerationLocalized
usingBlock:^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop){
if ([substring rangeOfString:#"ll" options:NSCaseInsensitiveSearch].location != NSNotFound)
/* do whatever */;
}];
As documented for -enumerateSubstringsInRange:options:usingBlock:, if you call it on a mutable string, you can safely mutate the string being enumerated within the enclosingRange. So, if you want to replace the matching words, you can with something like [aString replaceCharactersInRange:substringRange withString:replacementString].

Answer 2

The two ways I know of looping an array that will work for you are as follows:
NSArray *words = [sentence componentsSeparatedByCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
for (NSString *word in words)
{
NSString *transformedWord = [obj method:word];
}
and
NSArray *words = [sentence componentsSeparatedByCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
[words enumerateObjectsWithOptions:NSEnumerationConcurrent usingBlock:^(id word, NSUInteger idx, BOOL *stop){
NSString *transformedWord = [obj method:word];
}];
The other method, –makeObjectsPerformSelector:withObject:, won't work for you. It expects to be able to call [word method:obj] which is backwards from what you expect.

Answer 3

If you could write your criteria with regular expressions, then you could probably do a regular expression matching to fetch these words and then pass them to your convert: method.
You could also do a split of string into an array of words using componentsSeparatedByString: or componentsSeparatedByCharactersInSet:, then go over the words in the array and detect if they fit your criteria somehow. If they fit, then pass them to convert:.
Hope this helps.

Answer 4

As of iOS 12/macOS 10.14 the recommended way to do this is with the Natural Language framework.
For example:
import NaturalLanguage
let myString = "..."
let tokeniser = NLTokenizer(unit: .word)
tokeniser.string = myString
tokeniser.enumerateTokens(in: myString.startIndex..<myString.endIndex) { wordRange, attributes in
performActionOnWord(myString[wordRange])
return true // or return false to stop enumeration
}
Using NLTokenizer also has the benefit of allowing you to optionally specify the language of the string beforehand:
tokeniser.setLanguage(.hebrew)

Answer 5

I would recommend using a while loop to go through the string like this.
NSRange spaceRange = [sentenceContainingWords rangeOfString:#" "];
NSRange previousRange = (NSRange){0,0};
do {
NSString *wordString;
wordString = [sentenceContainingWord substringWithRange:(NSRange){previousRange.location+1,(spaceRange.location-1)-(previousRange.location+1)}];
//use the +1's to not include the spaces in the strings
[self convert:wordString];
previousRange = spaceRange;
spaceRange = [sentenceContainingWords rangeOfString:#" "];
} while(spaceRange.location != NSNotFound);
This code would probably need to be rewritten because its pretty rough, but you should get the idea.
Edit: Just saw Jacob Gorban's post, you should definitely do it like that.