OC 千位分隔符格式化数字

工作中总是碰到很多需求，比如金额需要以千位分隔的方式显示，这是OC版本转换方法，其它语言的可参考，代码如下：

/**
 转换目标字符串为千位分隔显示

 @param digitString 目标字符串
 @return 转换结果字符串
 */
+ (NSString *)groupedThousandsDigitStringWithStr:(NSString *)digitString {
    
    // 判断小数部位
    NSRange rangeOfPoint = [digitString rangeOfString:@"."];
    NSString *pointStr = @"";
    if (rangeOfPoint.length >= 1) {
        pointStr = [digitString substringFromIndex:rangeOfPoint.location];
    }
    
    // 去掉小数部位
    digitString = [digitString substringToIndex:rangeOfPoint.location];
    
    // 去掉小数位后长度小于3直接返回原字符
    if (digitString.length <= 3) return [digitString stringByAppendingString:pointStr];
    
    NSMutableString *processString = [NSMutableString stringWithString:digitString];
    
    NSInteger location = processString.length - 3;
    NSMutableArray *processArray = [NSMutableArray array];
    while (location >= 0) {
        NSString *temp = [processString substringWithRange:NSMakeRange(location, 3)];
        
        [processArray addObject:temp];
        if (location < 3 && location > 0) {
            NSString *t = [processString substringWithRange:NSMakeRange(0, location)];
            [processArray addObject:t];
        }
        location -= 3;
    }
    
    NSMutableArray *resultsArray = [NSMutableArray array];
    NSInteger k = 0;
    for (NSString *str in processArray) {
        k++;
        NSMutableString *tmp = [NSMutableString stringWithString:str];
        if (str.length > 2 && k < processArray.count ) {
            [tmp insertString:@"," atIndex:0];
            [resultsArray addObject:tmp];
        } else {
            [resultsArray addObject:tmp];
        }
    }
    
    NSMutableString *resultString = [NSMutableString string];
    for (NSInteger i = resultsArray.count - 1 ; i >= 0; i--) {
        NSString *tmp = [resultsArray objectAtIndex:i];
        [resultString appendString:tmp];
    }
    
    return [resultString stringByAppendingString:pointStr];
}