iPhone: Convert date string to a relative time stamp - iphone

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 '20 minutes ago' or '3 days ago'.
What's the best way to do this using Objective-C for the iPhone?

Answer 1

-(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";
}
}

Answer 2

Here are methods from Cocoa to help you to get relevant info (not sure if they are all available in coca-touch).
NSDate * today = [NSDate date];
NSLog(#"today: %#", today);
NSString * str = #"Thu, 21 May 09 19:10:09 -0700";
NSDate * past = [NSDate dateWithNaturalLanguageString:str
locale:[[NSUserDefaults
standardUserDefaults] dictionaryRepresentation]];
NSLog(#"str: %#", str);
NSLog(#"past: %#", past);
NSCalendar *gregorian = [[NSCalendar alloc]
initWithCalendarIdentifier:NSGregorianCalendar];
unsigned int unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit |
NSDayCalendarUnit |
NSHourCalendarUnit | NSMinuteCalendarUnit |
NSSecondCalendarUnit;
NSDateComponents *components = [gregorian components:unitFlags
fromDate:past
toDate:today
options:0];
NSLog(#"months: %d", [components month]);
NSLog(#"days: %d", [components day]);
NSLog(#"hours: %d", [components hour]);
NSLog(#"seconds: %d", [components second]);
The NSDateComponents object seems to hold the difference in relevant units (as specified).
If you specify all units you can then use this method:
void dump(NSDateComponents * t)
{
if ([t year]) NSLog(#"%d years ago", [t year]);
else if ([t month]) NSLog(#"%d months ago", [t month]);
else if ([t day]) NSLog(#"%d days ago", [t day]);
else if ([t minute]) NSLog(#"%d minutes ago", [t minute]);
else if ([t second]) NSLog(#"%d seconds ago", [t second]);
}
If you want to calculate yourself you can have a look at:
NSDate timeIntervalSinceDate
And then use seconds in the algorithm.
Disclaimer: If this interface is getting deprecated (I haven't checked), Apple's preferred way of doing this via NSDateFormatters, as suggested in comments below, looks pretty neat as well - I'll keep my answer for historical reasons, it may still be useful for some to look at the logic used.

Answer 3

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

Answer 4

In the interest of completeness, based on a #Gilean's answer, here's the complete code for a simple category on NSDate that mimics rails' nifty date helpers. For a refresher on categories, these are instance methods that you would call on NSDate objects. So, if I have an NSDate that represents yesterday, [myDate distanceOfTimeInWordsToNow] => "1 day".
Hope it's useful!
#interface NSDate (NSDate_Relativity)
-(NSString *)distanceOfTimeInWordsSinceDate:(NSDate *)aDate;
-(NSString *)distanceOfTimeInWordsToNow;
#end
#implementation NSDate (NSDate_Relativity)
-(NSString *)distanceOfTimeInWordsToNow {
return [self distanceOfTimeInWordsSinceDate:[NSDate date]];
}
-(NSString *)distanceOfTimeInWordsSinceDate:(NSDate *)aDate {
double interval = [self timeIntervalSinceDate:aDate];
NSString *timeUnit;
int timeValue;
if (interval < 0) {
interval = interval * -1;
}
if (interval< 60) {
return #"seconds";
} else if (interval< 3600) { // minutes
timeValue = round(interval / 60);
if (timeValue == 1) {
timeUnit = #"minute";
} else {
timeUnit = #"minutes";
}
} else if (interval< 86400) {
timeValue = round(interval / 60 / 60);
if (timeValue == 1) {
timeUnit = #"hour";
} else {
timeUnit = #"hours";
}
} else if (interval< 2629743) {
int days = round(interval / 60 / 60 / 24);
if (days < 7) {
timeValue = days;
if (timeValue == 1) {
timeUnit = #"day";
} else {
timeUnit = #"days";
}
} else if (days < 30) {
int weeks = days / 7;
timeValue = weeks;
if (timeValue == 1) {
timeUnit = #"week";
} else {
timeUnit = #"weeks";
}
} else if (days < 365) {
int months = days / 30;
timeValue = months;
if (timeValue == 1) {
timeUnit = #"month";
} else {
timeUnit = #"months";
}
} else if (days < 30000) { // this is roughly 82 years. After that, we'll say 'forever'
int years = days / 365;
timeValue = years;
if (timeValue == 1) {
timeUnit = #"year";
} else {
timeUnit = #"years";
}
} else {
return #"forever ago";
}
}
return [NSString stringWithFormat:#"%d %#", timeValue, timeUnit];
}
#end

Answer 5

There are already a lot of answers that come to the same solution but it can't hurt to have choices. Here's what I came up with.
- (NSString *)stringForTimeIntervalSinceCreated:(NSDate *)dateTime
{
NSDictionary *timeScale = #{#"second":#1,
#"minute":#60,
#"hour":#3600,
#"day":#86400,
#"week":#605800,
#"month":#2629743,
#"year":#31556926};
NSString *scale;
int timeAgo = 0-(int)[dateTime timeIntervalSinceNow];
if (timeAgo < 60) {
scale = #"second";
} else if (timeAgo < 3600) {
scale = #"minute";
} else if (timeAgo < 86400) {
scale = #"hour";
} else if (timeAgo < 605800) {
scale = #"day";
} else if (timeAgo < 2629743) {
scale = #"week";
} else if (timeAgo < 31556926) {
scale = #"month";
} else {
scale = #"year";
}
timeAgo = timeAgo/[[timeScale objectForKey:scale] integerValue];
NSString *s = #"";
if (timeAgo > 1) {
s = #"s";
}
return [NSString stringWithFormat:#"%d %#%# ago", timeAgo, scale, s];
}

Answer 6

I took Carl Coryell-Martin's code and made a simpler NSDate category that doesn't have warnings about the string formatting of the singulars, and also tidys up the week ago singular:
#interface NSDate (Extras)
- (NSString *)differenceString;
#end
#implementation NSDate (Extras)
- (NSString *)differenceString{
NSDate* date = self;
NSDate *now = [NSDate date];
double time = [date timeIntervalSinceDate:now];
time *= -1;
if (time < 60) {
int diff = round(time);
if (diff == 1)
return #"1 second ago";
return [NSString stringWithFormat:#"%d seconds ago", diff];
} else if (time < 3600) {
int diff = round(time / 60);
if (diff == 1)
return #"1 minute ago";
return [NSString stringWithFormat:#"%d minutes ago", diff];
} else if (time < 86400) {
int diff = round(time / 60 / 60);
if (diff == 1)
return #"1 hour ago";
return [NSString stringWithFormat:#"%d hours ago", diff];
} else if (time < 604800) {
int diff = round(time / 60 / 60 / 24);
if (diff == 1)
return #"yesterday";
if (diff == 7)
return #"a week ago";
return[NSString stringWithFormat:#"%d days ago", diff];
} else {
int diff = round(time / 60 / 60 / 24 / 7);
if (diff == 1)
return #"a week ago";
return [NSString stringWithFormat:#"%d weeks ago", diff];
}
}
#end

Answer 7

In Swift
Usage:
let time = NSDate(timeIntervalSince1970: timestamp).timeIntervalSinceNow
let relativeTimeString = NSDate.relativeTimeInString(time)
println(relativeTimeString)
Extension:
extension NSDate {
class func relativeTimeInString(value: NSTimeInterval) -> String {
func getTimeData(value: NSTimeInterval) -> (count: Int, suffix: String) {
let count = Int(floor(value))
let suffix = count != 1 ? "s" : ""
return (count: count, suffix: suffix)
}
let value = -value
switch value {
case 0...15: return "just now"
case 0..<60:
let timeData = getTimeData(value)
return "\(timeData.count) second\(timeData.suffix) ago"
case 0..<3600:
let timeData = getTimeData(value/60)
return "\(timeData.count) minute\(timeData.suffix) ago"
case 0..<86400:
let timeData = getTimeData(value/3600)
return "\(timeData.count) hour\(timeData.suffix) ago"
case 0..<604800:
let timeData = getTimeData(value/86400)
return "\(timeData.count) day\(timeData.suffix) ago"
default:
let timeData = getTimeData(value/604800)
return "\(timeData.count) week\(timeData.suffix) ago"
}
}
}

Answer 8

Use the NSDate class:
timeIntervalSinceDate
returns the interval in seconds.
Quick exercise to implement this in objective-c:
Get time "now" NSDate
Get the NSDate you wish to compare with
Get the interval in seconds using timeIntervalSinceDate
Then implement this pseudo code:
if (x < 60) // x seconds ago
else if( x/60 < 60) // floor(x/60) minutes ago
else if (x/(60*60) < 24) // floor(x/(60*60) hours ago
else if (x/(24*60*60) < 7) // floor(x(24*60*60) days ago
and so on...
then you need to decide whether a month is 30,31 or 28 days. Keep it simple - pick 30.
There might be a better way, but its 2am and this is the first thing that came to mind...

Answer 9

My solution:
- (NSString *) dateToName:(NSDate*)dt withSec:(BOOL)sec {
NSLocale *locale = [NSLocale currentLocale];
NSTimeInterval tI = [[NSDate date] timeIntervalSinceDate:dt];
if (tI < 60) {
if (sec == NO) {
return NSLocalizedString(#"Just Now", #"");
}
return [NSString stringWithFormat:
NSLocalizedString(#"%d seconds ago", #""),(int)tI];
}
if (tI < 3600) {
return [NSString stringWithFormat:
NSLocalizedString(#"%d minutes ago", #""),(int)(tI/60)];
}
if (tI < 86400) {
return [NSString stringWithFormat:
NSLocalizedString(#"%d hours ago", #""),(int)tI/3600];
}
NSDateFormatter *relativeDateFormatter = [[NSDateFormatter alloc] init];
[relativeDateFormatter setTimeStyle:NSDateFormatterNoStyle];
[relativeDateFormatter setDateStyle:NSDateFormatterMediumStyle];
[relativeDateFormatter setDoesRelativeDateFormatting:YES];
[relativeDateFormatter setLocale:locale];
NSString * relativeFormattedString =
[relativeDateFormatter stringForObjectValue:dt];
return relativeFormattedString;
}

Answer 10

Not sure why this isnt in cocoa-touch, i nice standard way of doing this would be great.
Set up some types to keep the data in, it will make it easier if you ever ned to localise it a bit more. (obviously expand if you need more time periods)
typedef struct DayHours {
int Days;
double Hours;
} DayHours;
+ (DayHours) getHourBasedTimeInterval:(double) hourBased withHoursPerDay:(double) hpd
{
int NumberOfDays = (int)(fabs(hourBased) / hpd);
float hoursegment = fabs(hourBased) - (NumberOfDays * hpd);
DayHours dh;
dh.Days = NumberOfDays;
dh.Hours = hoursegment;
return dh;
}
NOTE: I"m using an hour based calculation , as that is what my data is in. NSTimeInterval is second based. I also had to convert between the two.

Answer 11

I saw that there were several time ago functions in snippets of code on Stack Overflow and I wanted one that really gave the clearest sense of the time (since some action occurred). To me this means "time ago" style for short time intervals (5 min ago, 2 hours ago) and specific dates for longer time periods (April 15, 2011 instead of 2 years ago). Basically I thought Facebook did a really good job at this and I wanted to just go by their example (as I'm sure they out a lot of thought into this and it is very easy and clear to understand from the consumer perspective).
After a long time of googling I was pretty surprised to see that no one had implemented this as far as I could tell. Decided that I wanted it bad enough to spend the time writing and thought that I would share.
Hope you enjoy :)
Get the code here: https://github.com/nikilster/NSDate-Time-Ago