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iOS

Posted by Ryan Coughlin
Ryan Coughlin
1,677 Points

Finding nearest time - return index of array

I am looking to find the nearest time out of an array. My time in jSON is returned as milliseconds (epoch) - tideSummary.date.epoch

Stuck on the logic to find the closest time in the array compared to the current time. I can then grab that index and display the specific information. Thoughts on how I would do this?

So far I have:

  • Return the current time in ms as NSTimeInterval
  • Use that to find the delta of current time and tide[i] time

I would need to store the min somehow and return only the smallest delta value correct?

Any ideas?

1 Answer

John W
John W
21,558 Points
John W
John W
21,558 Points

Yes, smallest delta is good (you may also want to take absolute value as well).

NSTimeInterval by default is meant to be used as seconds, with sub-second intervals represented by subsequent decimal places. Best to stick to that for better documentation purposes.

A simply way to find the min would be a linear search: you iterate through the array, store the minimum (absolute) delta thus far and its corresponding index. Then when you hit the end, you have the min. Here's a somewhat self-explanatory code doing just that (assuming array stores NSDate objects as well)

NSTimeInterval minDelta = DBL_MAX; // largest double value
NSInteger minIndex = NSNotFound;
for ( NSInteger index = 0; i<array.count; i++ ) {
  NSTimeInterval newDelta = fabs( [(NSDate *)array[i] timeIntervalSinceNow]);
  if ( newDelta < minDelta ) {
    minDelta = newDelta;
    minIndex = index;
  } 
}

There's a slightly more Objective-C-esque way of doing this with NSPredicate, but that's probably too messy to explain here. Plus this code is probably more educational for you at this point.