mapreduce.php

<?
$record = [
    ["id" => "1",
     "name" => "東京都",
     "alias" => "東京",
    ],
    ["id" => "2",
     "name" => "神奈川県",
     "alias" => "神奈川"],
    ["id" => "3",
     "name" => "埼玉県",
     "alias" => "埼玉"],
    ["id" => "4",
     "name" => "千葉県",
     "alias" => "千葉"],
];

$func = function($value) {
    return [$value['id'] => $value['alias']];
};
$func2 = function ($result, $item) {
    if ($result == NULL) { $result = []; }
    $result = $result + $item;
    return $result;
};
$pref_array = array_map($func, $record);
$pref_name = array_reduce($pref_array, $func2);

print_r($pref_name);