- var_dump: documentation ( source)
- array_slice: documentation ( source)
- array_merge: documentation ( source)
<?php
$activities = [3];
$COUNT_PROFILES_IN_LETTER = 5;
$need = $COUNT_PROFILES_IN_LETTER - count($activities);
$additionalIds = [5, 7, 34, 198, 23783];
$activities = array_merge($activities, array_slice($additionalIds, 0, $need));
var_dump($activities);