Objective-C: Find numbers in string

I have a string that contains words as well as a number. How can I extract that number from the string?

NSString *str = @"This is my string. #1234";

I would like to be able to strip out 1234 as an int. The string will have different numbers and words each time I search it.

Ideas?

Solution 1:

Here's an NSScanner based solution:

// Input
NSString *originalString = @"This is my string. #1234";

// Intermediate
NSString *numberString;

NSScanner *scanner = [NSScanner scannerWithString:originalString];
NSCharacterSet *numbers = [NSCharacterSet characterSetWithCharactersInString:@"0123456789"];

// Throw away characters before the first number.
[scanner scanUpToCharactersFromSet:numbers intoString:NULL];

// Collect numbers.
[scanner scanCharactersFromSet:numbers intoString:&numberString];

// Result.
int number = [numberString integerValue];

(Some of the many) assumptions made here:

• Number digits are 0-9, no sign, no decimal point, no thousand separators, etc. You could add sign characters to the NSCharacterSet if needed.
• There are no digits elsewhere in the string, or if there are they are after the number you want to extract.
• The number won't overflow int.

Alternatively you could scan direct to the int:

[scanner scanUpToCharactersFromSet:numbers intoString:NULL];
int number;
[scanner scanInt:&number];

If the # marks the start of the number in the string, you could find it by means of:

[scanner scanUpToString:@"#" intoString:NULL];
[scanner setScanLocation:[scanner scanLocation] + 1];
// Now scan for int as before.

Solution 2:

Self contained solution:

+ (NSString *)extractNumberFromText:(NSString *)text
{
  NSCharacterSet *nonDigitCharacterSet = [[NSCharacterSet decimalDigitCharacterSet] invertedSet];
  return [[text componentsSeparatedByCharactersInSet:nonDigitCharacterSet] componentsJoinedByString:@""];
}

Handles the following cases:

• @"1234" → @"1234"
• @"001234" → @"001234"
• @"leading text get removed 001234" → @"001234"
• @"001234 trailing text gets removed" → @"001234"
• @"a0b0c1d2e3f4" → @"001234"

Hope this helps!

Solution 3:

You could use the NSRegularExpression class, available since iOS SDK 4.

Bellow a simple code to extract integer numbers ("\d+" regex pattern) :

- (NSArray*) getIntNumbersFromString: (NSString*) string {

  NSMutableArray* numberArray = [NSMutableArray new];

  NSString* regexPattern = @"\\d+";
  NSRegularExpression* regex = [[NSRegularExpression alloc] initWithPattern:regexPattern options:0 error:nil];

  NSArray* matches = [regex matchesInString:string options:0 range:NSMakeRange(0, string.length)];
  for( NSTextCheckingResult* match in matches) {
      NSString* strNumber = [string substringWithRange:match.range];
      [numberArray addObject:[NSNumber numberWithInt:strNumber.intValue]];
  }

  return numberArray; 
}