How to get the duplicate keys of multiple arrays? - php

Question

I know about array_intersect_key which returns duplicate keys of the first parameter in any of the following parameters.
However I was wondering which would be the easiest way to find duplicate keys across more than two arrays at once? Does PHP offer such a function or do I need to do it with multiple calls?
Given
$a1 = array('hello'=>1, 'tag'=>1);
$a2 = array('moin'=>1);
$a3 = array('moin'=>1, 'tag'=>1);
Duplicate keys across all three arrays are moin and tag.
I thought so far about calling array_intersect_keys on each possible pair of parameters (in a function accepting a 2-n number of arrays as parameters) but have problems to actually find all possible combinations. And perhaps there is a much more easier way to do this.

Answer 1

Here's a custom function I made which does what you're looking for:
function array_duplicate_keys()
{
$keys = array();
foreach(func_get_args() as $arr)
{
if(!is_array($arr))
{
continue;
}
foreach($arr as $key => $v)
{
if(!isset($keys[$key]))
{
$keys[$key] = -1;
}
$keys[$key]++;
}
}
return array_keys(array_filter($keys));
}
$a1 = array('hello'=>1, 'tag'=>1);
$a2 = array('moin'=>1);
$a3 = array('moin'=>1, 'tag'=>1);
/*
print_r(array_duplicate_keys($a1, $a2, $a3));
Array
(
[0] => tag
[1] => moin
)
*/

Answer 2

I think your idea is good - call it on every possible combination of arrays. Two nested for loops should be enough to get all combinations:
function array_duplicate_keys() {
$arrays = func_get_args();
$count = count($arrays);
$dupes = array();
// Stick all your arrays in $arrays first, then:
for ($i = 0; $i < $count; $i++) {
for ($j = $i+1; $j < $count; $j++) {
$dupes += array_intersect_key($arrays[$i], $arrays[$j]);
}
}
return array_keys($dupes);
}

Answer 3

$a1 = array('hello'=>1, 'tag'=>1);
$a2 = array('moin'=>1);
$a3 = array('moin'=>1, 'tag'=>1);
$all = array($a1, $a2, $a3);
function pair_duplicate_keys($arrays) {
$keys = array();
$result = array();
foreach ($arrays as $array) {
foreach ($array as $key => $value) {
if (!isset($keys[$key])) {
$keys[$key] = 1;
} else {
$result[$key] = 1;
}
}
}
return array_keys($result);
}
print_r(pair_duplicate_keys($all));
Output
Array
(
[0] => moin
[1] => tag
)

Answer 4

All you need is a simple call to array_merge function:
$a = array_merge($a1, $a2, $a3);
print_r($a);
OUTPUT
Array
(
[hello] => 1
[tag] => 1
[moin] => 1
)

Answer 5

Ugly, but does the job:
function array_duplicate_keys() {
return array_keys(array_filter(array_count_values(call_user_func_array('array_merge', array_map('array_keys', func_get_args()))), function ($num) {
return $num > 1;
}));
}
$a1 = array('hello'=>1, 'tag'=>1);
$a2 = array('moin'=>1);
$a3 = array('moin'=>1, 'tag'=>1);
print_r(
array_duplicate_keys($a1, $a2, $a3)
);
Output:
Array
(
[0] => tag
[1] => moin
)