如何在PHP函数中为每个帖子Id选择类别

$categories = [
    'post1' => '类别1',
    'post2' => '类别2',
    'post3' => '类别1',
    // 其他帖子ID和类别的映射关系
];

function getCategory($postId) {
    global $categories;
    
    if (array_key_exists($postId, $categories)) {
        return $categories[$postId];
    } else {
        return '未知类别';
    }
}

$postId = 'post1';
$category = getCategory($postId);
echo "帖子ID为{$postId}的类别是{$category}";