Merge array where duplicate in multidimensional array - php

Question

I've been trying to merge this array ONLY WHERE $array[4] exists more than one time, example: $array[4] == 'red' exactly twice. How can I merge only those arrays while keeping the others? I have made several attempts at this and I am willing to include my efforts if asked.
Consider this array:
array(3) {
[0]=>
array(5) {
[0]=>
string(3) "UID"
[1]=>
string(3) "532"
[2]=>
string(1) "2"
[3]=>
string(9) "Domain(s)"
[4]=>
string(20) "red"
}
[1]=>
array(5) {
[0]=>
string(3) "UID"
[1]=>
string(3) "532"
[2]=>
string(7) "License"
[3]=>
string(3) "Fee"
[4]=>
string(20) "red"
}
[2]=>
array(5) {
[0]=>
string(3) "UID"
[1]=>
string(3) "536"
[2]=>
string(7) "License"
[3]=>
string(3) "Fee"
[4]=>
string(16) " University Test"
}
}
TRYING TO ACHIEVE:
array(3) {
[0]=>
array(5) {
[0]=>
string(3) "UID"
[1]=>
string(3) "532"
[2]=>
string(1) "2"
[3]=>
string(9) "Domain(s)"
[4]=>
string(20) " red"
[5]=>
string(3) "Fee"
[6]=>
string(7) "License"
}
[1]=>
array(5) {
[0]=>
string(3) "UID"
[1]=>
string(3) "536"
[2]=>
string(7) "License"
[3]=>
string(3) "Fee"
[4]=>
string(16) " University Test"
}
}

Answer 1

foreach ($test as $item) {
if (!isset($merged[$item[4]])) {
// add the item to the merged array using key=$item[4]
$merged[$item[4]] = $item;
} else {
// merge the item with the item that is already in the array at key=$item[4]
$merged[$item[4]] = array_unique(array_merge($merged[$item[4]], $item));
// array_unique is necessary because array_merge will not overwrite numeric keys
}
}
// convert the keys back to numeric (if you care to)
$merged = array_values($merged);