Objective-C: Find numbers in string - iphone

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?

Answer 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.

Answer 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!

Answer 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;
}

Answer 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]];
}
}

Answer 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]);

Answer 6

Swift extension for getting number from string
extension NSString {
func getNumFromString() -> String? {
var numberString: NSString?
let thisScanner = NSScanner(string: self as String)
let numbers = NSCharacterSet(charactersInString: "0123456789")
thisScanner.scanUpToCharactersFromSet(numbers, intoString: nil)
thisScanner.scanCharactersFromSet(numbers, intoString: &numberString)
return numberString as? String;
}
}

Answer 7

NSPredicate is the Cocoa class for parsing string using ICU regular expression.