Date relative to now in string

[lexy0202]

Hi There,

Was wondering if anyone knew of a class which would give you a string telling you in 'human terms' how long ago a date was. For example on twitter/facebook when you see post dates like 2 minutes ago, or 3 hours ago, or 2 days ago... anyone know of a class which handles all the cases like this... or else how do I basically go about doing something like that with an NSDate??

Thanks in advance,
Alex

[Duncan C]

Originally Posted by lexy0202

Hi There,

Was wondering if anyone knew of a class which would give you a string telling you in 'human terms' how long ago a date was. For example on twitter/facebook when you see post dates like 2 minutes ago, or 3 hours ago, or 2 days ago... anyone know of a class which handles all the cases like this... or else how do I basically go about doing something like that with an NSDate??

Thanks in advance,
Alex

There's no single class to do this, but there are tools that make it fairly straightforward.

You need an NSCalendar object to define the calendar you're using. Most Western countries use the Gregorian calendar, so you probably want to create a gregorian calendar.

You could use the NSCalendar method components:fromDate:toDateptions. That will let you calculate a difference between dates using units you specify. The answer comes back and an NSDateComponents object, which gives you numbers of years, months, weeks, days, etc. You tell the components:fromDate:toDateptions method which units you want, and it calculates the answer in those units. There are then NSCalendar methods to convert NSDateComponents component values (months, days, years) to their string equivalents.

See the XCode docs on NSCalendar, NSDateComponents, and NSDate for more information. Its pretty well documented, and quite rich.

Edit: Make sure you search on "Calendrical Calculations" and read that whole chapter, and in particular the section titled "Temporal Differences". That section includes sample code that does almost exactly what you want.

[iSDK]

Came across it a while ago on StackOverflow.

-(NSString *)dateDiff:(NSString *)origDate {
    NSDateFormatter *df = [[NSDateFormatter alloc] init];
    [df setFormatterBehavior:NSDateFormatterBehavior10_4];
    [df setDateFormat:@"EEE, dd MMM yy HH:mm:ss VVVV"];
    NSDate *convertedDate = [df dateFromString:origDate];
    [df release];
    NSDate *todayDate = [NSDate date];
    double ti = [convertedDate timeIntervalSinceDate:todayDate];
    ti = ti * -1;
    if(ti < 1) {
        return @"never";
    } else      if (ti < 60) {
        return @"less than a minute ago";
    } else if (ti < 3600) {
        int diff = round(ti / 60);
        return [NSString stringWithFormat:@"%d minutes ago", diff];
    } else if (ti < 86400) {
        int diff = round(ti / 60 / 60);
        return[NSString stringWithFormat:@"%d hours ago", diff];
    } else if (ti < 2629743) {
        int diff = round(ti / 60 / 60 / 24);
        return[NSString stringWithFormat:@"%d days ago", diff];
    } else {
        return @"never";
    }   
}

[Duncan C]

Originally Posted by iSDK

Came across it a while ago on StackOverflow.

-(NSString *)dateDiff:(NSString *)origDate {
    NSDateFormatter *df = [[NSDateFormatter alloc] init];
    [df setFormatterBehavior:NSDateFormatterBehavior10_4];
    [df setDateFormat:@"EEE, dd MMM yy HH:mm:ss VVVV"];
    NSDate *convertedDate = [df dateFromString:origDate];
    [df release];
    NSDate *todayDate = [NSDate date];
    double ti = [convertedDate timeIntervalSinceDate:todayDate];
    ti = ti * -1;
    if(ti < 1) {
        return @"never";
    } else      if (ti < 60) {
        return @"less than a minute ago";
    } else if (ti < 3600) {
        int diff = round(ti / 60);
        return [NSString stringWithFormat:@"%d minutes ago", diff];
    } else if (ti < 86400) {
        int diff = round(ti / 60 / 60);
        return[NSString stringWithFormat:@"%d hours ago", diff];
    } else if (ti < 2629743) {
        int diff = round(ti / 60 / 60 / 24);
        return[NSString stringWithFormat:@"%d days ago", diff];
    } else {
        return @"never";
    }   
}

The code from Apple's documentation is simpler and more flexible:

NSDate *startDate = ...;
NSDate *endDate = ...;
 
NSCalendar *gregorian = [[NSCalendar alloc]
                 initWithCalendarIdentifier:NSGregorianCalendar];
 
NSUInteger unitFlags = NSMonthCalendarUnit | NSDayCalendarUnit;
 
NSDateComponents *components = [gregorian components:unitFlags
                                          fromDate:startDate
                                          toDate:endDate options:0];
NSInteger months = [components month];
NSInteger days = [components day];

It depends on what the OP wants. Do you want the results in just one unit, or in a group of units? Also, what about other calendars like the Buddhist, Muslim, Hebrew, Chinese traditional, etc.? Apple's code will give good results for those calendars as well, if you just create the right calendar object.