I'm using NSNumberFormatter to format float values as integer strings, i.e. omitting the fractional part. I find it odd, that numbers in range (-0.5, 0) *open interval end up as -0. As this value will be displayed to the user, I think that negative zero is not appropriate. I have experimented with various combinations of numberStyle and roundingMode without success.
Is there a way to configure the NSNumberFormatter to output them as 0, or do I have to resort to manual correction for that range?
I had to do correct this myself. I am using the NSNumberFormatter to display temperature with default numberStyle — NSNumberFormatterNoStyle which rounds the numbers to the whole integer, roundingMode set to NSNumberFormatterRoundHalfUp. In the end I did intercept the values in problematic range and round it myself:
- (NSString *)temperature:(NSNumber *)temperature
{
float f = [temperature floatValue];
if (f < 0 && f > -0.5)
temperature = [NSNumber numberWithLong:lround(f)];
return [self.temperatureFormatter stringFromNumber:temperature];
}
No, there is no way to configure it to do that.
In "10.4 mode", NSNumberFormatter basically just wraps CFNumberFormatter (although it's not a direct toll-free-bridged wrapping). You can look at the list of Number Formatter Property Keys and it's pretty clear that there's nothing that will do what you want. (It may be possible in "10.0" mode; it would take a bit of trial and error to find out. But I doubt you want to use that.)
So pre-rounding (as Justin Boo suggests) is probably your best option.
You could, of course, post-process instead. Exactly what you want to do probably depends on whether you want to also render -0.00 as 0.00, what you want to happen for localizations that don't use "-0", etc. The simplest case would be as simple as this:
#interface NSNumberFormatter (NegativeZero)
- (NSString *)stringFromNumberNoNegativeZero:(NSNumber *)number;
#end
#implementation NSNumberFormatter (NegativeZero)
- (NSString *)stringFromNumberNoNegativeZero:(NSNumber *)number {
NSString *s = [self stringFromNumber:number];
if ([s isEqualToString:#"-0"]) return #"0";
return s;
}
#end
But if you want anything more complicated, it'll get more complicated.
Related
I'm having a serious dispute with NSNumberFormatter, and even after going through its extensive documentation, I haven't quite been able to wrap my head around a pretty straightforward issue that I encountered. I hope you guys can help me out.
What I have: an NSDecimalNumber representing a calculation result, displayed in a UITextField
What I need: Scientific notation of that result.
What I'm doing:
-(void)setScientificNotationForTextField:(UITextField*)tf Text:(NSString*)text {
NSString* textBefore = text;
// use scientific notation, i.e. NSNumberFormatterScientificStyle
NSNumberFormatter* formatter = [[NSNumberFormatter alloc] init];
//[formatter setGeneratesDecimalNumbers:YES];
[formatter setNumberStyle:NSNumberFormatterScientificStyle];
NSDecimalNumber* number = (NSDecimalNumber*)[formatter numberFromString:text];
tf.text = [number descriptionWithLocale:[[Utilities sharedUtilities] USLocale]];
NSString* textAfter = tf.text;
// DEBUG
NSLog(#"setScientificNotation | text before = %#, text after = %#", textBefore, textAfter);
[formatter release];
}
What happens:
A certain result may be 0.0099. textBefore will hold that correct value. If I don't tell the formatter to generate decimal numbers (commented out in the above snippet), it will create an NSNumber from an NSDecimalNumber which creates a false result and turns textAfterinto 0.009900000000000001 - a rounding error due to the reduced precision of NSNumber over NSDecimalNumber.
If I do tell the NumberFormatter to generate decimals, it will still create the wrong result . And what's more, where before it would insert the exponent notation (e.g. "1.23456e-10"), it would now generate (and thus display) the full decimal number, which is not what I want.
Again, I'd like to have the formatter use NSDecimalNumber so it doesn't falsify results plus have exponent notation where necessary.
Am I using the class wrong? Did I misinterpret the documentation? Can someone explain why this happens and how I can create the behavior I want? I will of course continue researching and update if I find anything.
You can't just cast an NSNumber to an NSDecimalNumber and expect it to work. If your number is not too complex, you can ditch NSNumberFormatter and try using this instead:
NSDecimalNumber* number = [NSDecimalNumber decimalNumberWithString:text];
That will give you an actual NSDecimalNumber instance, with its precision.
Unfortunately, setGeneratesDecimalNumbers: doesn't work properly. It's a known bug.
If your number is too complex to work with decimalNumberWithString:, you're probably out of luck with Apple's APIs. Your only options are either parsing the string manually into something NSDecimalNumber can understand or performing some post-processing on the imprecise value given to you by NSNumberFormatter.
Finally, if you really want a number in scientific notation, why not just use the number formatter you just used? Just call stringFromNumber: to get the formatted value.
I have a value being stored as an NSDecimalNumber and when I convert it to a double it's losing precision.
For the current piece of data I'm debugging against, the value is 0.2676655. When I send it a doubleValue message, I get 0.267665. It's truncating instead of rounding and this is wreaking havoc with some code that uses hashes to detect data changes for a syncing operation.
The NSDecimalNumber instance comes from a third-party framework so I can't just replace it with a primitive double. Ultimately it gets inserted into an NSMutableString so I'm after a string representation, however it needs to be passed through a format specifier of "%.6lf", basically I need six digits after the decimal so it looks like 0.267666.
How can I accomplish this without losing precision? If there's a good way to format the NSDecimalNumber without converting to a double that will work as well.
The NSDecimalNumber instance comes from a third-party framework so I
can't just replace it with a primitive double.
Yes you can. NSDecimalNumber is an immutable subclass of NSNumber, which is a little too helpful when it comes to conversion:
double myDub = [NSDecimalNumber decimalNumberWithDecimal:[[NSNumber numberWithDouble:((double)0.2676655)] doubleValue]];
Ultimately it gets inserted into an NSMutableString so I'm after a
string representation, however it needs to be passed through a format
specifier of "%.6lf", basically I need six digits after the decimal so
it looks like 0.267666.
Double precision unfortunately does not round, but getting a string value that's off by one-millionth is not that big of a deal (I hope):
NSDecimalNumber *num = [NSDecimalNumber decimalNumberWithDecimal:[[NSNumber numberWithDouble:((double)0.2676655)] decimalValue]];
NSString *numString = [NSString stringWithFormat:#"%.6lf", [num doubleValue]];
NSLog(#"%#",numString);
I think that your are on a wrong path and somewhere lost in what to do.
First of all, keep in mind that in objective-c lond double is not supported, so you might better want to use something like %f instead of %lf.
[to be found in the documentation library under "Type encodings" of the objective c runtime programming guide]
Then I would rather expect that the value is show as being truncated, as the doubleValue returns an approximate value but the range you are using is still within the correct range.
You should use a simple formatter instead of moving numbers around, like:
// first line as an example for your real value
NSDecimalNumber *value = [NSDecimalNumber decimalNumberWithString:#"0.2676655"];
NSNumberFormatter *numFmt = [[NSNumberFormatter alloc] init];
[numFmt setMaximumFractionDigits:6];
[numFmt setMinimumFractionDigits:6];
[numFmt setMinimumIntegerDigits:1];
NSLog(#"Formatted number %#",[numFmt stringFromNumber:value]);
This has another benefit of using a locale aware formatter if desired. The result of the number formatter is the desired string.
I have a float value, that I would like to show it in format string and if it corresponds to an int, showing the integer, if not, showing it with one decimal.
Like this :
3.1
3
2.9
2.8
For now I'm stuck, in the concept, I'd do something like that :
float myFloat = 3.1
float mySecondFloat = 3
[NSString stringWithFormat:#"%g %g", myFloat, mySecondFloat];
My question is:
1/ the type format "%g" works in most cases but sometimes i have result shown like "0.600001" while in reality there should be 0.6 because all I do is 0.7 - 0.1.
Is there a kind of type cast for float at 1 decimal or maybe a bitwise operation to get rid of the final imprecision, or other way to make it works in 100% of cases ?
Thanks for your answers.
If your need absolute precision when working with decimal numbers, you may consider using the NSDecimalNumber class.
Number and Value Programming Topics: Using Decimal Numbers
Otherwise, the %.1g format specifier will be OK.
You have to use this code:
float myFloat = 3.1
float mySecondFloat = 3
[NSString stringWithFormat:#"%.1f %.1f", myFloat, mySecondFloat];
EDIT:
If I really want to print the integer value of a float, i would do it this way (ugly code)
int intValue = myFloatNumber/1;
NSString *string;
if(myFloatNumber == intValue)
{
string = [NSString stringWithFormat:#"%.0f", myFloatValue];
}
else
{
string = [NSString stringWithFormat:#"%.1f", myFloatValue];
}
Doing an integer division by 1, you automatically cast your float to an int.
Once you have the NSString *string you can concat it to your string.
Seeing others answers, it seems that there is no standard C formatter to achieve this.
I went following Nicolas answer (NSDecimalNumber), hence the solve flag. It worked fine indeed, but, in my (very simple) case it might be overkill. Giving it a second thought, if I had to do it again, I think that I would go using only NSNumberFormatter on a NSNumber (using numberWithFloat: method)
If it can help someone..
I'm struggling with this issue, and I couldn't find any resource for it :
I have an NSNumber that I want to display in an UITextField, so the user can edit it.
So I need to convert this NSNumber to an NSString, like this :
float value -> desired string value
1.0000000... -> 1
10.000000... -> 10
1.1230000... -> 1.123 or 1,123 depending on the locale
1000000.0... -> 1000000
I've tried to use NSNumberFormatter, but then I get spaces or comas for big numbers :
1000000.0... -> 1,000,000 or 1 000 000 depending on the locale
I also tried
[NSString stringWithFormat:#"%g", val]
But then for big numbers I have a scientific expression :
1000000.0 -> 1e+06
Did somebody have a successful experience with this ?
NSNumberFormatter has such method as :
- (void)setGroupingSeparator:(NSString *)string
I think, you can return to variant where you has:
1000000.0... -> 1,000,000 or 1 000 000 depending on the locale
and set additional parameter using that function:
[formatter setGroupingSeparator:#""];
Or moreover try this method:
[formatter setUsesGroupingSeparator:NO];
NSNumberFormatter is the solution, you were on the right path.
But:
the formatting it uses depends on the locale (either it uses the default locale if you don't override it, or you can set the locale used by the NSFormatter), because the NSLocale information also carries the Region Formatting info (formatting numbers using the US locale or the FR locale leads to different formats and different representations)
You can customize the formatting by tuning the options of NSNumberFormatter, like changing the grouping separators used, changing the decimal separator, etc.
This way you can really customize the way the NSNumberFormatter represents the numeric value into a string.
try converting nsnumber value to NSInteger or CGFloat and store it in the new variables. Then set the converted variables to uitextfield.
CGFloat floatNumber = [numberInNSNumber floatValue];
textfield.text = [NSString stringWithFormat:#"%0.2f",floatNumber];
I think it should work for you..!!
Have got an
NSString *str = #"12345.6789"
and want to find out if there is that "." character inside of it. I'm afraid that there are ugly char-encoding issues when I would just try to match an #"." against this? How would you do it to make sure it always finds a match if there is one?
I just need to know that there is a dot in there. Everything else doesn't matter.
You can use rangeOfString: message to get the range where your "." is.
The prototype is:
- (NSRange)rangeOfString:(NSString *)aString
You can find more info about this message in: Mac Dev Center
There would be something like this:
NSRange range;
range = [yourstring rangeOfString:#"."];
NSLog(#"Position:%d", range.location);
If you need to, there is another message ( rangeOfString:options: ) where you can add some options like "Case sensitive" and so on.
If [str rangeOfString:#"."] returns anything else than {NSNotFound, 0}, the search string was found in the receiver. There are no encoding issues as NSString takes care of encoding. However, there might be issues if your str is user-provided and could contain a different decimal separator (e.g., a comma). But then, if str really comes from the user, many other things could go wrong with that comparison anyway.
To check . symbol, it will be useful.
if ([[str componentsSeparatedByString:#"."] count]>1) {
NSLog(#"dot is there");
}else{
NSLog(#"dot is not there");
}
If what you really want to do is determine whether the string represents a number with a fractional part, a better solution is to feed the string to a number formatter, then examine the number's doubleValue to see whether it has a fractional part.
For the latter step, one way would be to use the modf function, which returns both the fractional part (directly) and the integral part (by reference). If the fractional part is greater than zero (or some appropriately small fraction below which you're willing to tolerate), then the number has a fractional part.
The reason why this is better is because not everybody writes decimal fractions in the “12345.6789” format. Some countries use a comma instead, and I'm sure that's not the only variation. Let the number formatter handle such cases for you.
I wrote a little method to make things a little more natural if you use this sort of thing a whole bunch in your project:
+(BOOL)seeIfString:(NSString*)thisString ContainsThis:(NSString*)containsThis
{
NSRange textRange = [[thisString lowercaseString] rangeOfString:[containsThis lowercaseString]];
if(textRange.location != NSNotFound)
return YES;
return NO;
}
Enjoy!