Objective-C: Find numbers in string

Question

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; 
}

Solution 4

Try this answer from Stack Overflow for a nice piece of C code that will do the trick:

for (int i=0; i<[str length]; i++) {
        if (isdigit([str characterAtIndex:i])) {
                [strippedString appendFormat:@"%c",[str characterAtIndex:i]];
        }
}

Solution 5

By far the best solution! I think regexp would be better, but i kind of sux at it ;-) this filters ALL numbers and concats them together, making a new string. If you want to split multiple numbers change it a bit. And remember that when you use this inside a big loop it costs performance!

    NSString *str= @"bla bla bla #123 bla bla 789";
    NSMutableString *newStr = [[NSMutableString alloc] init];;
    int j = [str length];
    for (int i=0; i<j; i++) {       
        if ([str characterAtIndex:i] >=48 && [str characterAtIndex:i] <=59) {
            [newStr appendFormat:@"%c",[str characterAtIndex:i]];
        }               
    }

    NSLog(@"%@  as int:%i", newStr, [newStr intValue]);

View more solutions

Comments

[Alex]

NSPredicate regular expression matching doesn't work on iOS SDK.

[Daniel Farrell]

Oh. Thanks, I didn't know that (spend most of my time in MacOS world).

[Nic Hubbard]

Great solution, this is just what I needed!

[Soumalya Banerjee]

Awesome. Great solution. Thanks.

[Jignesh B]

if i have multiple number at different place in string then it's return only first number

[ThomasW]

NSPredicate has been part of the iOS SDK since iOS 3.0.

[Yi Jiang]

This is the best and decent answer in this post. It is better than accepted answer.

[Yi Jiang]

Regular Expression is powerful. But in this simple case, I think @Zorayr 's answer is the best.

[Zorayr]

I wouldn't recommend using a c-style for loop here; this could cause a significant lag on larger strings, especially if executed on the main thread.

[Zorayr]

Regardless of my answer, I think using regex here might be an overkill and a bit more of a maintenance hazard; no one really understands regex and it's hard to debug.

[Farlei Heinen]

@Zorayr : I agree that it maybe is a little overkill, but I don't think it's a maintenance hazard. Actually it's really easy to add new functionality and a developer can reuse the pattern in any language that accepts regex.

[Farlei Heinen]

I add an example to make my answer more clear. It work for integer values. To expand to float values use this pattern: @"[\\d[.]]+"

[CyberMew]

Is it possible to strip the leading zeros as well?

[Marcus Adams]

Very nice. Don't fear the regex.