Collapse sequences of white space into a single character and trim string

This should do it...

NSString *s = @"this is    a  string    with lots  of     white space";
NSArray *comps = [s componentsSeparatedByCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];

NSMutableArray *words = [NSMutableArray array];
for(NSString *comp in comps) {
  if([comp length] > 1)) {
    [words addObject:comp];
  }
}

NSString *result = [words componentsJoinedByString:@" "];

Another option for regex is RegexKitLite, which is very easy to embed in an iPhone project:

[theString stringByReplacingOccurencesOfRegex:@" +" withString:@" "];

Here's a snippet from an NSString extension, where "self" is the NSString instance. It can be used to collapse contiguous whitespace into a single space by passing in [NSCharacterSet whitespaceAndNewlineCharacterSet] and ' ' to the two arguments.

- (NSString *) stringCollapsingCharacterSet: (NSCharacterSet *) characterSet toCharacter: (unichar) ch {
int fullLength = [self length];
int length = 0;
unichar *newString = malloc(sizeof(unichar) * (fullLength + 1));

BOOL isInCharset = NO;
for (int i = 0; i < fullLength; i++) {
    unichar thisChar = [self characterAtIndex: i];

    if ([characterSet characterIsMember: thisChar]) {
        isInCharset = YES;
    }
    else {
        if (isInCharset) {
            newString[length++] = ch;
        }

        newString[length++] = thisChar;
        isInCharset = NO;
    }
}

newString[length] = '\0';

NSString *result = [NSString stringWithCharacters: newString length: length];

free(newString);

return result;
}

Try This

NSString *theString = @"    Hello      this  is a   long       string!   ";

while ([theString rangeOfString:@"  "].location != NSNotFound) {
    theString = [theString stringByReplacingOccurrencesOfString:@"  " withString:@" "];
}

Alternative solution: get yourself a copy of OgreKit (the Cocoa regular expressions library).

• OgreKit (Japanese webpage -- code is in English)
• OgreKit (Google autotranslation):

The whole function is then:

NSString *theStringTrimmed =
   [theString stringByTrimmingCharactersInSet:
        [NSCharacterSet whitespaceAndNewlineCharacterSet]];
OGRegularExpression  *regex =
    [OGRegularExpression regularExpressionWithString:@"\s+"];
return [regex replaceAllMatchesInString:theStringTrimmed withString:@" "]);

Short and sweet.

If you're after the fastest solution, a carefully constructed series of instructions using NSScanner would probably work best but that'd only be necessary if you plan to process huge (many megabytes) blocks of text.

You can also use a simple while argument. There is no RegEx magic in there, so maybe it is easier to understand and alter in the future:

while([yourNSStringObject replaceOccurrencesOfString:@"  "
                         withString:@" "
                         options:0
                         range:NSMakeRange(0, [yourNSStringObject length])] > 0);