NSString: find range of word at index

Question

I have try'd some algorithms but no luck solving this problem.

Lets have a further explanation of the behaviour with an example

we have a string: @"example example"

So if i call rangeOfWordAtIndex:10 on the string.

the result would be: well the word @"example" at location 9 with a length 7.

It should not give @"example" at index 0 with a length of 7.

Here is the code i have produced so far:

#define unicode_space 32 // this is correct printed it out from code
@implementation NSString (wordAt)

- (NSRange) rangeOfWordAtIndex:(NSInteger) index
{
    NSInteger beginIndex = index;
    while(beginIndex > 0 && [self characterAtIndex:beginIndex-1] != unicode_space)
    {
        beginIndex--;
    }
    NSInteger endIndex = index;
    NSInteger sLenght = [self length];
    while (endIndex < sLenght && [self characterAtIndex:endIndex+1] != unicode_space)
    {
        endIndex++;
    }
    return NSMakeRange(beginIndex, endIndex - beginIndex);
}

@end

But it just doesn't work. without the +1 and -1 it keeps a space as part of a word.

And with it forgets the first character of the word.

Can someone please give some useful suggestion.

Answer 1

Detecting words is a bit more complex than finding U+0020 SPACE character. Fortunately, Foundation provides NSLinguisticTagger class that with full Unicode support. Here is how you find word and it's range at given index:

Objective-C

NSLinguisticTagger *tagger = [[NSLinguisticTagger alloc] initWithTagSchemes:@[ NSLinguisticTagSchemeTokenType ] options:kNilOptions];
tagger.string = @"Hello, World!";
NSRange range = NSMakeRange(0, 0);
NSString *tag = [tagger tagAtIndex:10 scheme:NSLinguisticTagSchemeTokenType tokenRange:&range sentenceRange:nil];

if ([tag isEqualToString:NSLinguisticTagWord]) {
    NSString *word = [tagger.string substringWithRange:range];
    // You have the word: "World"
}
else {
    // Punctuation, whitespace or other.
}

Swift

let tagger = NSLinguisticTagger(tagSchemes: [NSLinguisticTagSchemeTokenType], options: 0)
tagger.string = "Hello, World!"
var range : NSRange = NSRange(location: 0, length: 0)
let tag = tagger.tagAtIndex(10, scheme: NSLinguisticTagSchemeTokenType, tokenRange: &range, sentenceRange: nil)

if let string = tagger.string where tag == NSLinguisticTagWord {
    let word = (string as NSString).substringWithRange(range)
    // You have the word: "World"
}
else {
    // Punctuation, whitespace or other.
}