Objective c string formatter for distances

Question

I have a distance as a float and I'm looking for a way to format it nicely for human readers. Ideally, I'd like it to change from m to km as it gets bigger, and to round the number nicely. Converting to miles would be a bonus. I'm sure many people have had a need for one of these and I'm hoping that there's some code floating around somewhere.

Here's how I'd like the formats:

• 0-100m: 47m (as a whole number)
• 100-1000m: 325m or 320m (round to the nearest 5 or 10 meters)
• 1000-10000m: 1.2km (round to nearest with one decimal place)
• 10000m +: 21km

If there's no code available, how can I write my own formatter?

Thanks

Answer 1

None of these solutions really met what I was looking for, so I built on them:

#define METERS_TO_FEET  3.2808399
#define METERS_TO_MILES 0.000621371192
#define METERS_CUTOFF   1000
#define FEET_CUTOFF     3281
#define FEET_IN_MILES   5280

- (NSString *)stringWithDistance:(double)distance {
    BOOL isMetric = [[[NSLocale currentLocale] objectForKey:NSLocaleUsesMetricSystem] boolValue];

    NSString *format;

    if (isMetric) {
        if (distance < METERS_CUTOFF) {
            format = @"%@ metres";
        } else {
            format = @"%@ km";
            distance = distance / 1000;
        }
    } else { // assume Imperial / U.S.
        distance = distance * METERS_TO_FEET;
        if (distance < FEET_CUTOFF) {
            format = @"%@ feet";
        } else {
            format = @"%@ miles";
            distance = distance / FEET_IN_MILES;
        }
    }

    return [NSString stringWithFormat:format, [self stringWithDouble:distance]];
}

// Return a string of the number to one decimal place and with commas & periods based on the locale.
- (NSString *)stringWithDouble:(double)value {
    NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init];
    [numberFormatter setLocale:[NSLocale currentLocale]];
    [numberFormatter setNumberStyle:NSNumberFormatterDecimalStyle];
    [numberFormatter setMaximumFractionDigits:1];
    return [numberFormatter stringFromNumber:[NSNumber numberWithDouble:value]];
}

- (void)viewDidLoad {
    [super viewDidLoad];

    double distance = 5434.45;
    NSLog(@"%f meters is %@", distance, [self stringWithDistance:distance]);

    distance = 543.45;
    NSLog(@"%f meters is %@", distance, [self stringWithDistance:distance]);    

    distance = 234234.45;
    NSLog(@"%f meters is %@", distance, [self stringWithDistance:distance]);    
}

Answer 2

iOS 7 and OS X 10.9 introduced MKDistanceFormatter for formatting distances:

Code Example:

double myDistance = 21837.0f;

MKDistanceFormatter *df = [[MKDistanceFormatter alloc]init];
df.unitStyle = MKDistanceFormatterUnitStyleAbbreviated;

NSLog(@"myDistance is %@", [df stringFromDistance: myDistance]);

Update:

It seems that MKDistanceFormatter is rounding the input value somehow. E.g. when I set myDistance to 111.0 I get "100 m".