<?php

$array = array( 'api' => 1, 'class' => 2, 'fizz' => 3, 'buzz' => 4 );
$newAr = array();

foreach ( array( 'api', 'class' ) as $key ) {
  $newAr[$key] = $array[$key]; unset( $array[$key] );
}

print_r( $newAr );
print_r( $array );

Array
(
    [api] => 1
    [class] => 2
)
Array
(
    [fizz] => 3
    [buzz] => 4
)