Replace Western Arabic numerals with Persian digits

Question

I've written and used this code in my apps whenever needed to convert any Western Arabic numerals into Eastern Arabic (or better say, Persian/Farsi) numerals in any Persian text.

It works fine as expected, but I'm having a look at it now to reuse it, and I'm wondering if I could optimize this to reduced the repeated lines of code, and if so, how?

The header file, FarsiNumerals.h:

@interface FarsiNumerals : NSObject

+(NSString *)convertNumeralsToFarsi:(NSString *)englishNumeralString;

@end

and the implementation file, FarsiNumerals.m:

@implementation FarsiNumerals

+(NSString *)convertNumeralsToFarsi:(NSString *)englishNumeralString
{
    NSString *farsiNumeral;
    farsiNumeral = [englishNumeralString stringByReplacingOccurrencesOfString:@"1" withString:@"۱"];
    farsiNumeral = [farsiNumeral stringByReplacingOccurrencesOfString:@"2" withString:@"۲"];
    farsiNumeral = [farsiNumeral stringByReplacingOccurrencesOfString:@"3" withString:@"۳"];
    farsiNumeral = [farsiNumeral stringByReplacingOccurrencesOfString:@"4" withString:@"۴"];
    farsiNumeral = [farsiNumeral stringByReplacingOccurrencesOfString:@"5" withString:@"۵"];
    farsiNumeral = [farsiNumeral stringByReplacingOccurrencesOfString:@"6" withString:@"۶"];
    farsiNumeral = [farsiNumeral stringByReplacingOccurrencesOfString:@"7" withString:@"۷"];
    farsiNumeral = [farsiNumeral stringByReplacingOccurrencesOfString:@"8" withString:@"۸"];
    farsiNumeral = [farsiNumeral stringByReplacingOccurrencesOfString:@"9" withString:@"۹"];
    farsiNumeral = [farsiNumeral stringByReplacingOccurrencesOfString:@"0" withString:@"۰"];
    return farsiNumeral;
}

@end

It's a simple piece of code as you see; I'd call the method wherever needed and it'd replace the numerals with the correct ones for me for optimized text display purposes, and I'd like to know if I can somehow make this even shorter?

Answer 1

Simple transliteration may be insufficient. For example, I understand that the American English 10,000.00 should be ۱۰٬۰۰۰٫۰۰, but you probably do not want to replace all , and . throughout the text, but rather only within the context of numbers. (And, if we shift to other languages, the problem becomes even more complicated, because they might not even use the grouping separator every three digits.)

You might want to write a routine that does a regex search for Latin numbers (e.g., matching 10,000.00 for example, not the individual characters), then use a number formatter to convert the English number, and another number formatter to convert it to Farsi.

This is how one would use a number formatter:

NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
formatter.locale = [NSLocale localeWithLocaleIdentifier:@"fa"];

NSNumber *number = @(1234567890);
NSString *string = [formatter stringFromNumber:number]; // ۱۲۳۴۵۶۷۸۹۰

And, if you omit the locale altogether, it defaults to the user’s current locale (so Japanese users see Japanese, Chinese users see Chinese, etc.). This also handles thousandths and decimal separators unique to particular locales (e.g. with numberStyle of NSNumberFormatterDecimalStyle, for 1234.56, English users see “1,234.56” and German users see “1.234,56”.

FYI, you can change the numberStyle property to display it in other formats, too, e.g. NSNumberFormatterSpellOutStyle.

Formatters have all sorts of additional properties to control the format (e.g. minimum and maximum number of fraction digits, etc.). See the documentation for more information.

Answer 2

One recommendation I would have for this case is perhaps some equivalent of a dictionary (or hash map) for each definition of translation between an arabic numeral and a farsi numeral.

Looping through each element in either of those from there would certainly make the code more concise, albeit, I'm not entirely sure whether it would reduce any used space.

In general, turning this simple matter of translation into a hash map could have the advantage of making it clear what the code is doing and how it works.