- var_dump: documentation ( source)
- array_fill: documentation ( source)
<?php
$row = ['Rick', 'Lewi', 'Ferdi', 'Stefan'];
$mapping = ['Team1', 'Team2', 'Team3'];
$mappingCount = count($mapping);
$row = array_fill(0, $mappingCount, null) + $row;
var_dump($row);