I'm having problems with converting NSNumber to string and string to NSNumber.
Here's a sample problem:
NSString *stringValue = #"9.2";
NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
NSLog(#"stringvalue:%#",[[formatter numberFromString: stringValue] stringValue]);
Output will be:
stringvalue:9.199999999999999
I need to retrieve the original value, where, in the example should be 9.2.
On the contrary, when the original string is 9.4 the output is still 9.4.
Do you have any idea how to retrieve the original string value without NSNumber doing anything about it?
You are discovering that floating point numbers can't always be represented exactly. There are numerous posts about such issues.
If you need to get back to the original string, then keep the original string as your data and only convert to a number when you need to perform a calculation.
You may want to look into NSDecimalNumber. This may better fit your needs.
NSString *numStr = #"9.2";
NSDecimalNumber *decNum = [NSDecimalNumber decimalNumberWithString:numStr];
NSString *newStr = [decNum stringValue];
NSLog(#"decNum = %#, newStr = %#", decNum, newStr);
This gives 9.2 for both values.
Related
I used the localizedStringWithFormat: method on NSString class to convert a seven digit integer number to an NSString somewhere in my code and need to convert it back to an integer now.
As my App is localized for different regions with different separators after three digits (e.g. '.' in the U.S. and ',' in Germany), what's the best way to convert a localized NSString integer value to an integer?
I tried integerValue on my string as follows but it didn't work:
// Somewhere in code:
int num = 1049000;
NSString *myLocalizedNumString = [NSString localizedStringWithFormat:#"%d", num];
// myLocalizedNumString (U.S.): '1,049,000'
// myLocalizedNumString (Germany): '1.049.000'
// Somewhere else where I have a reference to my string but none to the num:
int restoredNum = [myLocalizedNumString integerValue];
// restoredNum isn't 1049000 (it's 0, the initial value)
What would be a good working way of doing it?
Despite its name NSNumberFormatter converts both ways, it is also a string parser. Using the method numberFromString after setting the number formatter’s numberStyle property to NSNumberFormatterDecimalStyle solves your problem.
The code might look as follows:
NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
formatter.numberStyle = NSNumberFormatterDecimalStyle;
NSInteger restoredNum = [[formatter numberFromString:myLocalizedNumString] integerValue];
If I do the following in Objective-C:
NSString *result = [NSString stringWithFormat:#"%1.1f", -0.01];
It will give result #"-0.0"
Does anybody know how I can force a result #"0.0" (without the "-") in this case?
EDIT:
I tried using NSNumberFormatter, but it has the same issue. The following also produces #"-0.0":
double value = -0.01;
NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init];
[numberFormatter setNumberStyle:NSNumberFormatterDecimalStyle];
[numberFormatter setMaximumFractionDigits:1];
[numberFormatter setMinimumFractionDigits:1];
NSString *result = [numberFormatter stringFromNumber:[NSNumber numberWithDouble:value]];
I wanted a general solution, independent of the configuration of the number formatter.
I've used a category to add the functionality to NSNumberFormater;
#interface NSNumberFormatter (PreventNegativeZero)
- (NSString *)stringFromNumberWithoutNegativeZero:(NSNumber *)number;
#end
With the implementation:
#implementation NSNumberFormatter (PreventNegativeZero)
- (NSString *)stringFromNumberWithoutNegativeZero:(NSNumber *)number
{
NSString *const string = [self stringFromNumber: number];
NSString *const negZeroString = [self stringFromNumber: [NSNumber numberWithFloat: -0.0f]];
if([string isEqualToString: negZeroString])
{
NSString *const posZeroString = [self stringFromNumber: [NSNumber numberWithFloat: 0.0]];
return posZeroString;
}
return string;
}
#end
How it works
The key feature is to ask the number formatter how it will format -0.0f (i.e., floating point minus zero) as an NSString so that we can detect this and take remedial action.
Why do this? Depending on the formatter configuration, -0.0f could be formatted as: #"-0", #"-0.0", #"-000", #"-0ºC", #"£-0.00", #"----0.0", #"(0.0)", #"😡𝟘.⓪零" really, pretty much anything. So, we ask the formatter how it would format -0.0f using the line: NSString *const negZeroString = [self stringFromNumber: [NSNumber numberWithFloat: -0.0f]];
Armed with the undesired -0.0f string, when an arbitrary input number is formatted, it can be tested to see if it is matches the undesirable -0.0f string.
The second important feature is that the number formatter is also asked to supply the replacement positive zero string. This is necessary so that as before, its formatting is respected. This is done with the line: [self stringFromNumber: [NSNumber numberWithFloat: 0.0]]
An optimisation that doesn't work
It's tempting to perform a numerical test yourself for whether the input number will be formatted as the -0.0f string, but this is extremely non trivial (ie, basically impossible in general). This is because the set of numbers that will format to the -0.0f string depend on the configuration of the formatter. If if happens to be rounding to the nearest million, then -5,000f as an input would be formatted as the -0.0f string.
An implementation error to avoid
When input that formats to the -0.0f string is detected, a positive zero equivalent output string is generated using [self stringFromNumber: [NSNumber numberWithFloat: 0.0]]. Note that, specifically:
The code formats the float literal 0.0f and returns it.
The code does not use the negation of the input.
Negating an input of -0.1f would result in formatting 0.1f. Depending on the formatter behaviour, this could be rounded up and result in #"1,000", which you don't want.
Final Note
For what it's worth, the approach / pattern / algorithm used here will translate to other languages and different string formatting APIs.
Use a NSNumberFormatter. In general, NSString formatting should not be used to present data to the user.
EDIT:
As stated in the question, this is not the correct answer. There is a number of solutions. It's easy to check for negative zero because it is defined to be equal to any zero (0.0f == -0.0f) but the actual problem is that a number of other values can be rounded to the negative zero. Instead of catching such values, I suggest postprocessing - a function that will check if the result contains only zero digits (skipping other characters). If yes, remove leading minus sign.
NSString *result = [NSString stringWithFormat:#"%1.1f", -0.01*-1];
If instead of a value you pass an instance you can check:
float myFloat = -0.01;
NSString *result = [NSString stringWithFormat:#"%1.1f", (myFloat<0? myFloat*-1:myFloat)];
Edit:
If you just want 0.0 as positive value:
NSString *result = [NSString stringWithFormat:#"%1.1f",(int)(myFloat*10)<0?myFloat:myFloat*-1];
Convert the number to NSString by taking the float or double value.
Convert the string back to NSNumber.
NSDecimalNumber *num = [NSDecimalNumber decimalNumberWithString:#"-0.00000000008"];
NSString *st2 = [NSString stringWithFormat:#"%0.2f", [num floatValue]];
NSDecimalNumber *result = [NSDecimalNumber decimalNumberWithString:st2]; //returns 0
The NSNumberFormatter has two methods convert from Number to String, and from String to Number. What if we use method (Number) -> String? twice?
public extension NumberFormatter {
func stringWithoutNegativeZero(from number: NSNumber) -> String? {
string(from: number)
.flatMap { [weak self] string in self?.number(from: string) }
.flatMap { [weak self] number in self?.string(from: number) }
}
}
I was making a basic method that takes a Flickr image URL and returns the image's ID.
I'm passing the method the NSString #"http://farm6.staticflickr.com/5183/5629026092_c6762a118f".
The goal is to return the int: 5629026092, which is in the image's URL and is the image's ID.
Here is my method:
-(int)getImageIDFromFlickrURL:(NSString *)imageURL{
NSArray *objectsInURLArray = [imageURL componentsSeparatedByString:#"/"];
NSString *lastObjectInFlickrArray = [objectsInURLArray lastObject];
NSArray *dirtyFlickrIdArray = [lastObjectInFlickrArray componentsSeparatedByString:#"_"];
NSString *flickIDString = [dirtyFlickrIdArray objectAtIndex:0];
NSLog(#"flickr id string: %#",flickIDString);
int flickrID = [flickIDString intValue];
NSLog(#"id: %i",flickrID);
return flickrID;
}
The output in the console is:
2012-05-26 13:30:25.771 TestApp[1744:f803] flickr id string: 5629026092
2012-05-26 13:30:25.773 TestApp[1744:f803] id: 2147483647
Why is calling intValue deforming the actual number?
Use long long instead, your number is greater than int can handle (max being 2147483647 as you can see in your second log)
Your value is too big to represent in 32 bits. The biggest value you can store in a signed 32 bit integer (int) is 2147483647. For unsigned ints, it's 4294967295. You need to convert to a long long integer to represent a number as big as 5629026092.
You'll probably need to create a number formatter for that. I'm no expert on number formatters, and always have to dig out the documentation to figure out how to use them.
I just tried it, and this code works:
NSString *numberString = #"5629026092";
NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
NSNumber *number = [formatter numberFromString: numberString];
long long value = [number longLongValue];
NSLog(#"%# = %qi", numberString, value);
[formatter release];
You could also convert the string to a C string and use scanf, come to think of it.
Easy ^^: INT_MAX Maximum value for a variable of type int. 2147483647
I found this to be a convenient way to do it:
NSString *flickIDString = [dirtyFlickrIdArray objectAtIndex:0]; // read some huge number into a string
// read into a NSNumber object or a long long variable. you choose
NSNumber *flickIDNumber = flickIDString.longLongValue;
long long flickIDLong = flickIDString.longLongValue;
I have a NSDictionary that contains data converted from json data, like {"message_id":21}.
then I use NSNumber *message_id = [dictionary valueForKey:#"message_id"] to get the data.
but when I use this message_id,
Message *message = [NSEntityDescription ....
message.messageId = message_id;
I got the runtime error, assigning _NSCFString to NSNumber,
so I have to use NSNumberFormatter to do the conversion.
NSString *messageId = [dictionary valueForKey:#"message_id"];
NSNumberFormatter * f = [[NSNumberFormatter alloc] init];
[f setNumberStyle:NSNumberFormatterNoStyle];
message.messageId = [f numberFromString:messageId];
this code works.
but when I was debugging, I saw message_id of
NSNumber *message_id = [dictionary valueForKey:#"message_id"]
has a valid value, 21.
Can anyone see the problem here?
You are trying to save a NSString to a NSNumber. If you want it as an NSNumber you can do:
NSNumber *message_id = [NSNumber numberWithInt:[[dictionary valueForKey:#"message_id"] intValue]];
This should solve your problem.
What library are you using to do the conversion? {"message_id":21} means that an NSNumber with a value of 21 should be returned as an NSNumber, {"message_id":"21"} should return it as an NSString.
Using a number formatter is total overkill. Use the method "integerValue" which works just fine both with NSString* and with NSNumber* - you will get the integer 21, whether the object is NSString or NSNumber. The formatter code will obviously run into trouble if your object is an NSNumber and not an NSString.
So: message.messageId = [[NSNumber numberWithInteger:[messageId integerValue]];
I'd probably add a category to NSDictionary
(NSNumber*)nsIntegerNumberForKey:(NSString*)key
which handles the situations where the key is not present, or where the value is a null value or a dictionary or array, so you can use it everywhere you need an NSNumber with an integer value from a JSON document and have error checking everywhere.
Read here SAVING JSON TO CORE DATA and JSON official page
The JSON standard is quite clear about how to distinguish strings from
numbers– basically, strings are surrounded by quotes and numbers are
not. JSON web services however, are not always good about following this requirement. And even when they are, they are not always consistent from one record to another.
So if you have receive NSNumber where NSString is preferred, you must inspect and fix yourself
I have a string called realEstateWorth with a value of $12,000,000.
I need this same string to remain a string but for any number (such as the one above) to be displayed as $12 MILLION or $6 MILLION. The point is it needs the words "MILLION" to come after the number.
I know there is nsNumberFormatter that can convert strings into numbers and vice versa but can it do what I need?
If anyone has any ideas or suggestions, it would be much appreciated.
Thank you!
So as I see it, you have two problems:
You have a string representation of something that's actually a number
You (potentially) have a number that you want formatted as a string
So, problem #1:
To convert a string into a number, you use an NSNumberFormatter. You've got a pretty simple case:
NSNumberFormatter *f = [[NSNumberFormatter alloc] init];
[f setNumberStyle:NSNumberFormatterCurrencyStyle];
NSNumber *n = [f numberFromString:#"$12,000,000"];
// n is 12000000
That was easy! Now problem #2:
This is trickier, because you want a mixed spell-out style. You could consider using an NSNumberFormatter again, but it's not quite right:
[f setNumberStyle:NSNumberFormatterSpellOutStyle];
NSString *s = [f stringFromNumber:n];
// s is "twelve million"
So, we're closer. At this point, you could perhaps maybe do something like:
NSInteger numberOfMillions = [n integerValue] / 1000000;
if (numberOfMillions > 0) {
NSNumber *millions = [NSNumber numberWithInteger:numberOfMillions];
NSString *numberOfMillionsString = [f stringFromNumber:millions]; // "twelve"
[f setNumberStyle:NSNumberFormatterCurrencyStyle];
NSString *formattedMillions = [f stringFromNumber:millions]; // "$12.00"
if ([s hasPrefix:numberOfMillionsString]) {
// replace "twelve" with "$12.00"
s = [s stringByReplacingCharactersInRange:NSMakeRange(0, [numberOfMillionsString length]) withString:formattedMillions];
// if this all works, s should be "$12.00 million"
// you can use the -setMaximumFractionDigits: method on NSNumberFormatter to fiddle with the ".00" bit
}
}
However
I don't know how well this would work in anything other than english. CAVEAT IMPLEMENTOR
Worst case scenario, you could implement a category on NSString to implement the behaviour you want.
In the method that you would do in that category you could take an NSNumberFormatter to bring that string to a number and by doing some modulo operation you could define if you need the word Million, or Billion, etc. and put back a string with the modulo for Million or other way you need it to be.
That way you could just call that method on your NSString like this :
NSString *humanReadable = [realEstateWorth myCustomMethodFromMyCategory];
And also.
NSString are immutable, so you can't change it unless you assign a new one to your variable.
I'd recommend storing this value as an NSNumber or a float. Then you could have a method to generate an NSString to display it like:
- (NSString*)numberToCurrencyString:(float)num
{
NSString *postfix = #"";
if (num > 1000000000)
{
num = num / 1000000000;
postfix = #" Billion";
}
else if (num > 1000000)
{
num = num / 1000000;
postfix = #" Million";
}
NSString *currencyString = [NSString stringWithFormat:#"%.0f%#", num, postfix];
return currencyString;
}
Note: Your question states that your input needs to remain a string. That's fine. So you'd need to 1.) first parse the number out of the string and 2.) then reconvert it to a string from a number. I've shown how to do step 2 of this process.