compare values from multidimensional array and add key to array - php

Question

Array
(
[681074CRPAK4] => Array
(
[0] => 681074
[1] => 681074CRPAK4
[2] => 5602385431605
)
[681520XXXP6L] => Array
(
[0] => 681520
[1] => 681520XXXP6L
[2] => 5602385667394
)
[681530XXXP6V] => Array
(
[0] => 681530
[1] => 681530XXXP6V
[2] => 5602385667417
)
[681530XXXP6W] => Array
(
[0] => 681530
[1] => 681530XXXP6W
[2] => 5602385667424
)
[681530XXXP6X] => Array
(
[0] => 681530
[1] => 681530XXXP6X
[2] => 5602385667400
)
)
I want to compare the value of key[0] of each array.
If they are the same then I would like to add a new key[3] to each array with an id.
This is an array of variable products if the product has the same key[0] then its the same product with different variations.
If the key[0] is different from the previous then add id+1, in this example, I would like to end up with:
Array
(
[681074CRPAK4] => Array
(
[0] => 681074
[1] => 681074CRPAK4
[2] => 5602385431605
[3] => 1
)
[681520XXXP6L] => Array
(
[0] => 681520
[1] => 681520XXXP6L
[2] => 5602385667394
[3] => 2
)
[681530XXXP6V] => Array
(
[0] => 681530
[1] => 681530XXXP6V
[2] => 5602385667417
[3] => 3
)
[681530XXXP6W] => Array
(
[0] => 681530
[1] => 681530XXXP6W
[2] => 5602385667424
[3] => 3
)
[681530XXXP6X] => Array
(
[0] => 681530
[1] => 681530XXXP6X
[2] => 5602385667400
[3] => 3
)
)
can you guys help me with this?
I tried this:
but does not work
foreach ($new as $current_key => $current_array) {
foreach ($new as $search_key => $search_array) {
$ref1 = $current_array[0];
$ref2 = $search_array[0];
if (($search_key != $current_key) and ($ref1 == $ref2)) {
$current_array[3] = $p_id_product;
}
else{
$current_array[3] = $p_id_product++;
}
}
}

Answer 1

Assuming you have already sorted the array by the initial index, so at least they are grouped:
<?php
$data =
[
[
'foo',
'spam',
'bar',
],
[
'foo',
'eggs',
],
[
'bar',
'ham'
],
];
$output = [];
$counter = 0;
$last = null;
foreach($data as $k => $v) {
if($last !== $v[0])
$counter++;
$v[3] = $counter;
$output[$k] = $v;
$last = $v[0];
}
var_export($output);
Output:
array (
0 =>
array (
0 => 'foo',
1 => 'spam',
2 => 'bar',
3 => 1,
),
1 =>
array (
0 => 'foo',
1 => 'eggs',
3 => 1,
),
2 =>
array (
0 => 'bar',
1 => 'ham',
3 => 2,
),
)