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

Question

Consider the following example:

"    Hello      this  is a   long       string!   "

I want to convert that to:

"Hello this is a long string!"

Answer 1

OS X 10.7+ and iOS 3.2+

Use the native regexp solution provided by hfossli.

Otherwise

Either use your favorite regexp library or use the following Cocoa-native solution:

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:@" "];

Answer 2

Regex and NSCharacterSet is here to help you. This solution trims leading and trailing whitespace as well as multiple whitespaces.

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

NSString *squashed = [original stringByReplacingOccurrencesOfString:@"[ ]+"
                                                         withString:@" "
                                                            options:NSRegularExpressionSearch
                                                              range:NSMakeRange(0, original.length)];

NSString *final = [squashed stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];

Logging final gives

"Hello this is a long string!"

Possible alternative regex patterns:

• Replace only space: [ ]+
• Replace space and tabs: [ \\t]+
• Replace space, tabs and newlines: \\s+

Performance rundown

• This solution: 7.6 seconds
• Splitting, filtering, joining (Georg Schölly): 13.7 seconds

Ease of extension, performance, number lines of code and the number of objects created makes this solution appropriate.

Answer 3

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 4

With a regex, but without the need for any external framework:

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

theString = [theString stringByReplacingOccurrencesOfString:@" +" withString:@" "
                       options:NSRegularExpressionSearch
                       range:NSMakeRange(0, theString.length)];

Answer 5

A one line solution:

NSString *whitespaceString = @" String with whitespaces ";

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

Answer 6

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:@" "];

Answer 7

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

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

Answer 8

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 9

Try This

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

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

Answer 10

Following two regular expressions would work depending on the requirements

1. @" +" for matching white spaces and tabs
2. @"\\s{2,}" for matching white spaces, tabs and line breaks

Then apply nsstring's instance method stringByReplacingOccurrencesOfString:withString:options:range: to replace them with a single white space.

e.g.

[string stringByReplacingOccurrencesOfString:regex withString:@" " options:NSRegularExpressionSearch range:NSMakeRange(0, [string length])];

Note: I did not use 'RegexKitLite' library for the above functionality for iOS 5.x and above.

Answer 11

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);

Answer 12

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 13

according from @Mathieu Godart is best answer, but some line is missing , all answers just reduce space between words , but when if have tabs or have tab in place space , like this: " this is text \t , and\tTab between , so on " in three line code we will : the string we want reduce white spaces

NSString * str_aLine = @"    this is text \t , and\tTab between      , so on    ";
// replace tabs to space
str_aLine = [str_aLine stringByReplacingOccurrencesOfString:@"\t" withString:@" "];
// reduce spaces to one space
str_aLine = [str_aLine stringByReplacingOccurrencesOfString:@" +" withString:@" "
                                                    options:NSRegularExpressionSearch
                                                      range:NSMakeRange(0, str_aLine.length)];
// trim begin and end from white spaces
str_aLine = [str_aLine stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];

the result is

"this is text , and Tab between , so on"

without replacing tab the resul will be:

"this is text    , and  Tab between , so on"