```
Simple array arithmetic:
```

A more compact way of adding or subtracting the elements at identical keys...

<?php

function array_add($a1, $a2) { $aRes = $a1;

foreach (array_slice(func_get_args(), 1) as $aRay) {

foreach (array_intersect_key($aRay, $aRes) as $key => $val) $aRes[$key] += $val;

$aRes += $aRay; }

return $aRes; }

function array_subtract($a1, $a2) { $aRes = $a1;

foreach (array_slice(func_get_args(), 1) as $aRay) {

foreach (array_intersect_key($aRay, $aRes) as $key => $val) $aRes[$key] -= $val;

foreach (array_diff_key($aRay, $aRes) as $key => $val) $aRes[$key] = -$val; }

return $aRes; }

Example:

$a1 = array(9, 8, 7);

$a2 = array(1=>7, 6, 5);

$a3 = array(2=>5, 4, 3);

$aSum = array_add($a1, $a2, $a3);

$aDiff = array_subtract($a1, $a2, $a3);

?>

To make a similar function, array_concatenate(), change only the first of the two '+=' in array_add() to '.='

Csaba Gabor from Vienna