<?php

$array = array(
0 => "bar",
1 => "foo",
"a" => "zai"
);

var_dump(array_combine($array, $array));

array(3) {
  ["bar"]=>
  string(3) "bar"
  ["foo"]=>
  string(3) "foo"
  ["zai"]=>
  string(3) "zai"
}