Computes the difference of arrays by using a callback function for data comparison

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- PHP Manual
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- Computes the difference of arrays by using a callback function for data comparison

# array_udiff

(PHP 5, PHP 7, PHP 8)

array_udiff — Computes the difference of arrays by using a callback function for data comparison

### Description

array_udiff(array `$array`, array `...$arrays`, callable `$value_compare_func`): array

Computes the difference of arrays by using a callback function for data comparison. This is unlike array_diff() which uses an internal function for comparing the data.

### Parameters

`array`

  The first array.

`arrays`

  Arrays to compare against.

`value_compare_func`

  The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.

  callback(mixed `$a`, mixed `$b`): int
  Caution

  Returning non-integer values from the comparison function, such as float, will result in an internal cast to int of the callback's return value. So values such as `0.99` and `0.1` will both be cast to an integer value of `0`, which will compare such values as equal.

  Caution

  The sorting callback must handle any value from any array in any order, regardless of the order they were originally provided. This is because each individual array is first sorted before being compared against other arrays. For example:

      <?php
      $arrayA = ["string", 1];
      $arrayB = [["value" => 1]];
      // $item1 and $item2 can be any of "string", 1 or ["value" => 1]
      $compareFunc = static function ($item1, $item2) {
          $value1 = is_string($item1) ? strlen($item1) : (is_array($item1) ? $item1["value"] : $item1);
          $value2 = is_string($item2) ? strlen($item2) : (is_array($item2) ? $item2["value"] : $item2);
          return $value1 <=> $value2;
      };
      ?>

### Return Values

Returns an array containing all the values of `array` that are not present in any of the other arguments.

### Examples

Example #1 array_udiff() example using stdClass Objects

    <?php
    // Arrays to compare
    $array1 = array(new stdClass, new stdClass,
                    new stdClass, new stdClass,
                   );

    $array2 = array(
                    new stdClass, new stdClass,
                   );

    // Set some properties for each object
    $array1[0]->width = 11; $array1[0]->height = 3;
    $array1[1]->width = 7;  $array1[1]->height = 1;
    $array1[2]->width = 2;  $array1[2]->height = 9;
    $array1[3]->width = 5;  $array1[3]->height = 7;

    $array2[0]->width = 7;  $array2[0]->height = 5;
    $array2[1]->width = 9;  $array2[1]->height = 2;

    function compare_by_area($a, $b) {
        $areaA = $a->width * $a->height;
        $areaB = $b->width * $b->height;

        if ($areaA < $areaB) {
            return -1;
        } elseif ($areaA > $areaB) {
            return 1;
        } else {
            return 0;
        }
    }

    print_r(array_udiff($array1, $array2, 'compare_by_area'));
    ?>

The above example will output:

    Array
    (
        [0] => stdClass Object
            (
                [width] => 11
                [height] => 3
            )

        [1] => stdClass Object
            (
                [width] => 7
                [height] => 1
            )

    )

Example #2 array_udiff() example using DateTime Objects

    <?php
    class MyCalendar {
        public $free = array();
        public $booked = array();

        public function __construct($week = 'now') {
            $start = new DateTime($week);
            $start->modify('Monday this week midnight');
            $end = clone $start;
            $end->modify('Friday this week midnight');
            $interval = new DateInterval('P1D');
            foreach (new DatePeriod($start, $interval, $end) as $freeTime) {
                $this->free[] = $freeTime;
            }
        }

        public function bookAppointment(DateTime $date, $note) {
            $this->booked[] = array('date' => $date->modify('midnight'), 'note' => $note);
        }

        public function checkAvailability() {
            return array_udiff($this->free, $this->booked, array($this, 'customCompare'));
        }

        public function customCompare($free, $booked) {
            if (is_array($free)) $a = $free['date'];
            else $a = $free;
            if (is_array($booked)) $b = $booked['date'];
            else $b = $booked;
            if ($a == $b) {
                return 0;
            } elseif ($a > $b) {
                return 1;
            } else {
                return -1;
            }
        }
    }

    // Create a calendar for weekly appointments
    $myCalendar = new MyCalendar;

    // Book some appointments for this week
    $myCalendar->bookAppointment(new DateTime('Monday this week'), "Cleaning GoogleGuy's apartment.");
    $myCalendar->bookAppointment(new DateTime('Wednesday this week'), "Going on a snowboarding trip.");
    $myCalendar->bookAppointment(new DateTime('Friday this week'), "Fixing buggy code.");

    // Check availability of days by comparing $booked dates against $free dates
    echo "I'm available on the following days this week...\n\n";
    foreach ($myCalendar->checkAvailability() as $free) {
        echo $free->format('l'), "\n";
    }
    echo "\n\n";
    echo "I'm busy on the following days this week...\n\n";
    foreach ($myCalendar->booked as $booked) {
        echo $booked['date']->format('l'), ": ", $booked['note'], "\n";
    }
    ?>

The above example will output:

    I'm available on the following days this week...

    Tuesday
    Thursday

    I'm busy on the following days this week...

    Monday: Cleaning GoogleGuy's apartment.
    Wednesday: Going on a snowboarding trip.
    Friday: Fixing buggy code.

### Notes

> Note: Please note that this function only checks one dimension of a n-dimensional array. Of course you can check deeper dimensions by using `array_udiff($array1[0], $array2[0], "data_compare_func");`.

### See Also

- array_diff() - Computes the difference of arrays
- array_diff_assoc() - Computes the difference of arrays with additional index check
- array_diff_uassoc() - Computes the difference of arrays with additional index check which is performed by a user supplied callback function
- array_udiff_assoc() - Computes the difference of arrays with additional index check, compares data by a callback function
- array_udiff_uassoc() - Computes the difference of arrays with additional index check, compares data and indexes by a callback function
- array_intersect() - Computes the intersection of arrays
- array_intersect_assoc() - Computes the intersection of arrays with additional index check
- array_uintersect() - Computes the intersection of arrays, compares data by a callback function
- array_uintersect_assoc() - Computes the intersection of arrays with additional index check, compares data by a callback function
- array_uintersect_uassoc() - Computes the intersection of arrays with additional index check, compares data and indexes by separate callback functions