Find the nearest time from list of array

One of the best ways to compare times is to convert your strings to times using strtotime().

// Original array of date strings
$dates = array(
  '08/29/2013 08:00',
  '08/29/2013 08:10',
  '08/29/2013 08:11',
  '08/29/2013 12:20',
  '08/29/2013 12:21',
  '08/29/2013 12:21',
  '08/29/2013 17:30',
);

// Make a new array of time stamps based on your strings
$dates_dt = array();
foreach($dates as $date)
  $dates_dt[] = strtotime($date);

// Same idea with the dates you want to look at
$date_last1 = strtotime('08/29/2013 08:00');
$date_last2 = strtotime('08/29/2013 13:00');
$date_first1 = strtotime('08/29/2013 12:00');
$date_first2 = strtotime('08/29/2013 17:00');

Here's the magic - some pretty simple functions that return the closest date before (or the first entry), and the closest after (or the last) in your array.

function dateBefore($date, $dateArray){
  $prev = $dateArray[0];
  foreach( $dateArray as $d ){
      if( $d >= $date )
          return date("Y-m-d H:i", $prev);
      $prev = $d;
  }
}

function dateAfter($date, $dateArray){
  foreach( $dateArray as $d ){
      if( $d > $date )
          return date("Y-m-d H:i", $d);
  }
  return date("Y-m-d H:i", end($dateArray));
}

echo dateBefore($date_last1, $dates_dt); // Outputs: 2013-08-29 08:00
echo dateBefore($date_last2, $dates_dt); // Outputs: 2013-08-29 12:21

echo dateAfter($date_first1, $dates_dt); // Outputs: 2013-08-29 12:20
echo dateAfter($date_first2, $dates_dt); // Outputs: 2013-08-29 17:30

http://codepad.org/cBYPuowt

Note Probably a good idea to sort the array of times as well so they're for sure in order.

foreach($dates as $date)
  $dates_dt[] = strtotime($date);

// Add sort here
sort($dates_dt);

http://codepad.org/jZPIEeJS

You can convert all of the string timestamps to long values (milliseconds since 1970 epoch). Then just calculate the delta for relevant values (greater than 08/29/2013 08:00, for instance) compared to the upper limit (08/29/2013 13:00, for instance). The smallest delta is the closest to the upper limit. The greatest delta is furthest.

This is how you calculate the seconds since epoch: http://php.net/manual/en/function.strtotime.php

$nearest = $dates[0];
$now = time();
for ($i = 0; $i < count($dates); $i++) {
  $date = $dates[$i];
  $timestamp = strtotime($date);
  if (abs(strtotime($date) - $now) < abs(strtotime($nearest) - $now))
    $nearest = $date;
}
echo $nearest;