Question

I need a way to merge

Array(
  [0] => Array
     (
      [event_id] => 1
      [time] => '21:00pm'
      [day] => 'Monday'
     )
  [1] => Array
    (
      [event_id] => 2
      [time] => '18:00pm'
      [day] => 'Monday'
     )
  [2] => Array
    (
      [event_id] => 3
      [time] => '21:00pm'
      [day] => 'Tuesday'
     )
 )

into:

Array (
  [0] => Array
      (
          [event_id] => Array
                (
                 [0] => 1
                 [1] => 2
                )
          [time] => Array
               (
                 [0] => '21:00pm'
                 [1] => '18:00pm'
                )
          [day] => 'Monday'
      )
   [1] => Array
     (
          [event_id] => 3
          [time] => '21:00pm'
          [day] => 'Tuesday'
     )
)

So the new array is grouped by the day key and if the values are different between the merged arrays then the merged value becomes an array.

Answer 1

This should work.

$output = getMergedArray($input); // $input is your sample array

function getMergedArray($input_array) {
  $output_array = array();
  foreach ($input_array as $key => $value) {
    $event_id = $value['event_id'];
    $time = $value['time'];
    $day = $value['day'];
    $day_id = getDay($output_array, $day);
    if (count($output_array) > 0 && $day_id >= 0) {
      if (!is_array($output_array[$day_id]['event_id'])) {
        $output_array[$day_id]['event_id'] = array($output_array[$day_id]['event_id']);
        $output_array[$day_id]['time'] = array($output_array[$day_id]['time']);
      }
      array_push($output_array[$day_id]['event_id'],$event_id);
      array_push($output_array[$day_id]['time'],$time);
    } else {
      $output_array[] = $value;
    }
  }
  return $output_array;
}

function getDay($output_array, $day) {
  if (count($output_array) > 0)
    foreach($output_array as $key => $value)
      if ($value['day'] == $day)
        return $key;

  return -1;
}