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copied!<p>If you have a lot of these date comparisons, then the calls to <code>calendar:components:fromDate</code> start to take up a lot of time. According to some profiling I have done, they seem to be quite expensive.</p> <p>Say you are trying to determine which from some array of dates, say <code>NSArray *datesToCompare</code>, are the same day as some given day, say <code>NSDate *baseDate</code>, then you can use something like the following (partly adapted from an answer above):</p> <pre><code>NSDate *baseDate = [NSDate date]; NSArray *datesToCompare = [NSArray arrayWithObjects:[NSDate date], [NSDate dateWithTimeIntervalSinceNow:100], [NSDate dateWithTimeIntervalSinceNow:1000], [NSDate dateWithTimeIntervalSinceNow:-10000], [NSDate dateWithTimeIntervalSinceNow:100000], [NSDate dateWithTimeIntervalSinceNow:1000000], [NSDate dateWithTimeIntervalSinceNow:50], nil]; // determine the NSDate for midnight of the base date: NSCalendar* calendar = [NSCalendar currentCalendar]; NSDateComponents* comps = [calendar components:(NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit) fromDate:baseDate]; NSDate* theMidnightHour = [calendar dateFromComponents:comps]; // set up a localized date formatter so we can see the answers are right! NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init]; [dateFormatter setDateStyle:NSDateFormatterMediumStyle]; [dateFormatter setTimeStyle:NSDateFormatterMediumStyle]; // determine which dates in an array are on the same day as the base date: for (NSDate *date in datesToCompare) { NSTimeInterval interval = [date timeIntervalSinceDate:theMidnightHour]; if (interval >= 0 && interval < 60*60*24) { NSLog(@"%@ is on the same day as %@", [dateFormatter stringFromDate:date], [dateFormatter stringFromDate:baseDate]); } else { NSLog(@"%@ is NOT on the same day as %@", [dateFormatter stringFromDate:date], [dateFormatter stringFromDate:baseDate]); } } </code></pre> <p>Output:</p> <pre><code>Nov 23, 2011 1:32:00 PM is on the same day as Nov 23, 2011 1:32:00 PM Nov 23, 2011 1:33:40 PM is on the same day as Nov 23, 2011 1:32:00 PM Nov 23, 2011 1:48:40 PM is on the same day as Nov 23, 2011 1:32:00 PM Nov 23, 2011 10:45:20 AM is on the same day as Nov 23, 2011 1:32:00 PM Nov 24, 2011 5:18:40 PM is NOT on the same day as Nov 23, 2011 1:32:00 PM Dec 5, 2011 3:18:40 AM is NOT on the same day as Nov 23, 2011 1:32:00 PM Nov 23, 2011 1:32:50 PM is on the same day as Nov 23, 2011 1:32:00 PM </code></pre>

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