Extract post category except one category

Question

My posts are in two categories - one that defines their type eg. article or review and the other defines the topic - tablets,smartphones,smartwatches, etc.

How can I get the current post's category ID for its topic - i.e. whether it's a tablet, smartphone or smartwatch.

If I do get_the_category( $post->ID ); I suppose it'll return all categories the post is in, but how do I filter out the article or review categories out?

Example: Post ABC is in categories article with ID=1 and tablets with ID=10 how can I extract on the tablets ID=10 category without the article one?

Answer 1

You can simply loop over the categories that you don't need. get_the_category() return an array of categories that the post belongs to.

With that in mind, you can do the following: (Just remember to change 21 and 41 to your desired ID's)

$categories = get_the_category();
foreach ( $categories as $category ) {
    if( 21 ===  $category->cat_ID || 41 === $category->cat_ID ) {
        continue;
    }else{
        echo $category->cat_ID . '</br>';
    }
}