Objective C strip out whitespace from NSString

Question

How do I strip out the white space chars from an NSString ?
Consider the following example:

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

I want to convert that to: "Hello this is a long string!". I have tried a function like this, but it's not working:

-(NSString *)cleanupString:(NSString *)theString
{
  // Remove extra whitespace
  NSString *theStringTrimmed = [theString stringByTrimmingCharactersInSet: [NSCharacterSet whitespaceAndNewlineCharacterSet]];
  // Split it on whitespace
  NSArray *wordsInStringArray = [theStringTrimmed componentsSeparatedByString:@"  "];
  // Now join it together again
  NSString *returnString = [[NSString alloc] init];
  for ( NSString* thisElement in wordsInStringArray ) 
      {
      returnString = [ returnString stringByAppendingString:[NSString stringWithFormat:@"%@_",thisElement] ];
      }
     return returnString;
 }

Answer 1

C has no good, simple way of dealing with string manipulation like this. Your answer is probably the best/easiest your going to get with it. However, instead of separating your words by some arbitrary-length white space string, use componentsSeparatedByCharactersInSet and use the whitespaceCharacterSet again. That should give you the desired results.

Answer 2

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;
}

Answer 3

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] > )) {
    [words addObject:comp];
  }
}

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

Answer 4

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.

Answer 5

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

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

Answer 6

Actually there's a very simple solution to that:

NSString *string = @" spaces in front and at the end ";
NSString *trimmedString = [string stringByTrimmingCharactersInSet:
                                  [NSCharacterSet whitespaceAndNewlineCharacterSet]];
NSLog(trimmedString)

(Source)

Answer 7

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

NSCharacterSet *whitespaces = [NSCharacterSet whitespaceCharacterSet];
NSPredicate *noEmptyStrings = [NSPredicate predicateWithFormat:@"SELF != ''"];

NSArray *parts = [theString componentsSeparatedByCharactersInSet:whitespaces];
NSArray *filteredArray = [parts filteredArrayUsingPredicate:noEmptyStrings];
theString = [filteredArray componentsJoinedByString:@" "];

Don't use complex solutions if there's an easy one.

Answer 8

A one line solution:

NSString *whitespaceString = @" String with whitespaces ";

NSString *trimmedString = [whitespaceString stringByReplacingOccurrencesOfString:@" " withString:@""];