Question

I’m looking for a way to search an arbitrary long string (10000 characters) and find the number of times a specific keyword is repeated in the string. How can this be done?

I have this method, that pretty much counts the number of fragments left after the string is split around keywords, but it is not case insensitive.

-(void)countKeywords
{
    NSArray* components = [self.salesCopy componentsSeparatedByString:@"search term"];

    NSLog(@"search term number found: %i",components.count);


}

What’s a better way to count the number of keywords within a string?

Answer 1

Splitting the string, counting parts, and throwing them away is not efficient. Searching for substring repeatedly without creating new objects would definitely be more efficient. Since the string is relatively long, you may benefit from implementing an advanced string search algorithm, for example Knuth-Morris-Pratt, to significantly decrease your search time.

Here is an implementation that should be faster than your splitting code:

NSString *str = @"Hello sun, hello bird, hello my lady! Hello breakfast, May I buy you again tomorrow?";
NSRange r = NSMakeRange(0, str.length);
int count = 0;
for (;;) {
    r = [str rangeOfString:@"hello" options:NSCaseInsensitiveSearch range:r];
    if (r.location == NSNotFound) {
        break;
    }
    count++;
    r.location++;
    r.length = str.length - r.location;
}
NSLog(@"%d", count);