<?php
$results = [
['id' => 1, 'breakdown' => [1, 2]],
['id' => 2, 'breakdown' => [5, 6]],
['id' => 3, 'breakdown' => [7]],
];
$extraAccessorials = [9];
$breakdownRaw = [];
foreach ($results as $key => $value) {
// $extraAccessorials should be assigned at some point before.
$breakdownRaw[] = $extraAccessorials;
}
$results[$key]['breakdown'] = \
array_merge($results[$key]['breakdown'], ... $breakdownRaw);
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