Objective-C: format numbers to ordinals: 1, 2, 3, .. to 1st, 2nd, 3rd

You could use ICU, which includes a way of doing what you describe:

http://icu-project.org/apiref/icu4c/classRuleBasedNumberFormat.html

You don't say what context you're using Objective-C in, but if you're writing for Cocoa, ICU is actually present. However, reaching down to talk to it directly can be a bit tricky.

[edited to link to someone who actually seems to have figured out how to build ICU and link it]

How to build ICU so I can use it in an iPhone app?

The solution is immediately available from NSNumberFormatter:

- (NSString *)getOrdinalStringFromInteger:(NSInteger)integer
{
    NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
    [formatter setLocale:[NSLocale currentLocale]];
    [formatter setNumberStyle:NSNumberFormatterOrdinalStyle];
    return [formatter stringFromNumber:[NSNumber numberWithInteger:integer]];
}

You need a rule set for each language you want to support. Any language is asking too much: they are all wildly different. First, create a rule set class which holds the regular and the exception cases for a given language. That class needs a single method that takes a number and returns a string suffix (or the number plus the suffix.) Create rule set instances (statically) for each language you care about.

Then create a category on NSNumber that returns a suffix pulled from the appropriate rule set for whatever language the user needs (system locale, or some choice they make, or case by case.)

Each language has different rules, of course. For example, English is relatively complicated: 1st, 2nd, 3rd, 4th, 5th, ... 20th and then it starts again at st, nd, rd, th... Unit 1s, 2s, 3s and 4s are always special cases. Zero is 'th' (zeroth, hundredth, millionth etc.)

French is different. 1er, then it's x ième all the way up. (These are usually abbreviated to just 're' and 'e', making French quite easy.)

Japanese gets very odd. Cardinal 1, 2, 3, 4: (ichi, ni, san, yon) becomes tsuichi, futsuka, mikka and yokka. Those aren't suffixes though: the numbers are named differently when they're used as ordinals. Luckily, because that's incredibly confusing, you can just stick a kanji 'kai' character (which looks like a box in box) after the number and everyone knows what you mean.

Have you taken a look at TTTOrdinalNumberFormatter which is in FormatterKit? It works great, and I'm pretty sure it's exactly what you're looking for.

---

Here's an example taken from the kit:

TTTOrdinalNumberFormatter *ordinalNumberFormatter = [[TTTOrdinalNumberFormatter alloc] init];
[ordinalNumberFormatter setLocale:[NSLocale currentLocale]];
[ordinalNumberFormatter setGrammaticalGender:TTTOrdinalNumberFormatterMaleGender];
NSNumber *number = [NSNumber numberWithInteger:2];
NSLog(@"%@", [NSString stringWithFormat:NSLocalizedString(@"You came in %@ place!", nil), [ordinalNumberFormatter stringFromNumber:number]]);

Assuming you've provided localized strings for "You came in %@ place!", the output would be:

* English: "You came in 2nd place!"
* French: "Vous êtes venu à la 2eme place!"
* Spanish: "Usted llegó en 2.o lugar!"