Question

is there a sensible way of removing ALL fields from an array APART from ones that I specify?

I’m thinking something along the lines of array_diff could work, but I only want to list the field keys that I want to allow, and then say ‘drop everything else’. What’s the best way of doing that?

Many thanks

Answer 1

array_intersect_key() should work if copying the array is OK.

$arr = array(
    'A' => 'alpha',
    'B' => 'bravo',
    'C' => 'charlie',
    'D' => 'delta'
);

$allowedKeys = array('B', 'C');

print_r(array_intersect_key($arr, array_flip($allowedKeys)));

# Array
# (
#    [B] => bravo
#    [C] => charlie
# )

Otherwise, you can use a foreach loop:

foreach ($arr as $key => $value) {
    if (!in_array($key, $allowedKeys)) {
        unset($arr[$key]);
    }
}