New Array的键应该是另一个Array的值

I want to create new array.
Value of element in array should be blank.
Key of array should another array's value.

$Oldarr =  Array
(
    [0] => Webseite,
    [1] => Bestellung,
    [2] => Verkäufer,
    [3] => Käufer,
    [4] => Warenwert,
    [5] => Lieferkosten,
    [6] => Produktname,
    [7] => Article Nr,
    [8] => Anzahl
);

And New array shoud be

$Newarr =  Array
(
    ['Bestellung'] => '',
    ['Verkäufer'] => '',
    ['Käufer'] => '',
    ['Warenwert'] => '',
    ['Lieferkosten'] => '',
    ['Produktname'] => '',
    ['Article Nr'] => '',
    ['Anzahl'] => ''
);

use array_flip to make key as values and values as keys.

$newarr = array_flip($Oldarr);

If you need to set blank values as well then you can use array_fill_keys like:

$newarr = array_flip($Oldarr);
$newarr = array_fill_keys($newarr, null);//for null values
$newarr = array_fill_keys($newarr, '');//for empty string values

Edited:

only array_fill_keys will work in your scenario (credit goes to @Sougata Bose who commented here)

$newarr = array_fill_keys($Oldarr, '');//for empty string values

You can use following code:

$new = array_flip($Oldarr);
$new = array_fill_keys($Oldarr,'');