Assuming you are trying to map Columns from the resulting rows such that:

Row | Column 1 | Column 2
1   | Value 1  | Value 2
2   | Value 2  | Value 2

Results in:

$rows = array(
    1 => array(
        'Column 1' => 'Value 1',
        'Column 2' => 'Value 2'
    ),
    2 => array(
        'Column 1' => 'Value 1',
        'Column 2' => 'Value 2'
    ),
);

If your PDO returns the values in numerical position, you can do this:

$columns = array(
    'Column 1',
    'Column 2'
);

$rows = array_map(function($row) use ($columns) {
    return array_combine($columns, $row);
}, $resultSet);

Or, if the $resultSet is associative, and you want to keep the names:

$columns = array_flip(array(
    'Column 1',
    'Column 2'
));

$rows = array_map(function($row) use ($columns) {
    return array_intersect_key($row, $columns);
}, $resultSet);

Assuming you are trying to map Columns from the resulting rows such that:

Row | Column 1 | Column 2
1   | Value 1  | Value 2
2   | Value 2  | Value 2

Results in:

$rows = array(
    1 => array(
        'Column 1' => 'Value 1',
        'Column 2' => 'Value 2'
    ),
    2 => array(
        'Column 1' => 'Value 1',
        'Column 2' => 'Value 2'
    ),
);

If your PDO returns the values in numerical position, you can do this:

$columns = array(
    'Column 1',
    'Column 2'
);

$rows = array_map(function($row) use ($columns) {
    return array_combine($columns, $row);
}, $resultSet);

Or, if the $resultSet is associative, and you want to keep the names:

$columns = array_flip(array(
    'Column 1',
    'Column 2'
));

$rows = array_map(function($row) use ($columns) {
    return array_intersect_key($row, $columns);
}, $resultSet);

OR, if your PDO returns them in an Associative array, but the Column names need to be change:

$columns = array(
    'Column 1' => 'Key 1',
    'Column 2' => 'Key 1'
);

$rows = array_map(function($row) use ($columns) {
    $return = array();
    foreach($columns as $from => $to) {
        $return[$to] = !empty($row[$from]) ? $row[$from] : NULL;
    }
    return $return;
}, $resultSet);

That last one would work for either situation, really, as it will take the value at $row[$from] and place it at $result[$to], which would account for numerical indices or string indices. Also, the empty() check will suppress PHP errors, and will ensure that you have a value at each position.