5.9.1. Calculating the Sum of an Array

$sum = array_sum(array);

For example:

$scores  = array(98, 76, 56, 80);
$total   = array_sum($scores);
// $total = 310

5.9.2. Merging Two Arrays

$merged = array_merge(array1, array2 [, array ... ])

$first  = array('hello', 'world');      // 0 => 'hello', 1 => 'world'
$second = array('exit',  'here');       // 0 => 'exit',  1 => 'here'
$merged = array_merge($first, $second);
// $merged = array('hello', 'world', 'exit', 'here')

If a string key from an earlier array is repeated, the earlier value is replaced by the later value:

$first  = array('bill' => 'clinton', 'tony' => 'danza');
$second = array('bill' => 'gates',   'adam' => 'west');
$merged = array_merge($first, $second);
// $merged = array('bill' => 'gates', 'tony' => 'danza', 'adam' => 'west')

5.9.3. Calculating the Difference Between Two Arrays

$diff = array_diff(array1, array2 [, array ... ]);

For example:

$a1 = array('bill', 'claire', 'elle', 'simon', 'judy');
$a2 = array('jack', 'claire', 'toni');
$a3 = array('elle', 'simon',  'garfunkel');
// find values of $a1 not in $a2 or $a3
$diff = array_diff($a1, $a2, $a3);
// $diff is array('bill', 'judy');

Values are compared using ===, so 1 and "1" are considered different. The keys of the first array are preserved, so in $diff the key of 'bill' is 0 and the key of 'judy' is 4.

5.9.4. Filtering Elements from an Array

$filtered = array_filter(array, callback);

Each value of array is passed to the function named in callback. The returned array contains only those elements of the original array for which the function returns a true value. For example:

function is_odd ($element) {
  return $element % 2;
}
$numbers = array(9, 23, 24, 27);
$odds    = array_filter($numbers, 'is_odd');
// $odds is array(0 => 9, 1 => 23, 3 => 27)

As you see, the keys are preserved. This function is most useful with associative arrays.