iPhone: Convert date string to a relative time stamp

Question

I\'ve got a timestamp as a string like:

Thu, 21 May 09 19:10:09 -0700

and I\'d like to convert it to a relative time stamp like

Answer 1

I can't edit yet, but I took Gilean's code and made a couple of tweaks and made it a category of NSDateFormatter.

It accepts a format string so it will work w/ arbitrary strings and I added if clauses to have singular events be grammatically correct.

Cheers,

Carl C-M

@interface NSDateFormatter (Extras)
+ (NSString *)dateDifferenceStringFromString:(NSString *)dateString
                                  withFormat:(NSString *)dateFormat;

@end

@implementation NSDateFormatter (Extras)

+ (NSString *)dateDifferenceStringFromString:(NSString *)dateString
                                  withFormat:(NSString *)dateFormat
{
  NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
  [dateFormatter setFormatterBehavior:NSDateFormatterBehavior10_4];
  [dateFormatter setDateFormat:dateFormat];
  NSDate *date = [dateFormatter dateFromString:dateString];
  [dateFormatter release];
  NSDate *now = [NSDate date];
  double time = [date timeIntervalSinceDate:now];
  time *= -1;
  if(time < 1) {
    return dateString;
  } else if (time < 60) {
    return @"less than a minute ago";
  } else if (time < 3600) {
    int diff = round(time / 60);
    if (diff == 1) 
      return [NSString stringWithFormat:@"1 minute ago", diff];
    return [NSString stringWithFormat:@"%d minutes ago", diff];
  } else if (time < 86400) {
    int diff = round(time / 60 / 60);
    if (diff == 1)
      return [NSString stringWithFormat:@"1 hour ago", diff];
    return [NSString stringWithFormat:@"%d hours ago", diff];
  } else if (time < 604800) {
    int diff = round(time / 60 / 60 / 24);
    if (diff == 1) 
      return [NSString stringWithFormat:@"yesterday", diff];
    if (diff == 7) 
      return [NSString stringWithFormat:@"last week", diff];
    return[NSString stringWithFormat:@"%d days ago", diff];
  } else {
    int diff = round(time / 60 / 60 / 24 / 7);
    if (diff == 1)
      return [NSString stringWithFormat:@"last week", diff];
    return [NSString stringWithFormat:@"%d weeks ago", diff];
  }   
}

@end