How to exclude tags and categories from a function?

Question

I'm trying to get a piece of code to filter out tags and categories when it generates its list. Right now it generates all posts by most recent (although it's a little buggy so if someone knows a better piece of code to use with ajax load more, I'm all ears.

Here's the code:

<div class="mcol-posts ajax-posts">
  <?php
    //BLOG POSTS
      $postsPerPage = 5;
      $args = array(
      'posts_per_page' => $postsPerPage
      $loop = new WP_Query($args);
      while ($loop->have_posts()) : $loop->the_post(); 
      get_template_part( 'template-parts/content', 'excerpt' );
      endwhile;
      wp_reset_postdata();                          
   ?>
</div>

I want to add something like this (could be different, but this is what I'm working with right now), in order to exclude any posts with tags or categories I don't want. It would be ideal to exclude more than one tag and more than one category, or to NULL either/both if not needed.

if ($cat_not_in) {
  $args['category__not_in'] = array($cat_not_in);
}
if ($tag_not_in) {
  $args['tag__not_in'] = array($tag_not_in);
}

Answer 1

I don't know how the structure of $cat_not_in looks like but make sure that that variable is not an array. If $cat_not_in is an array then you could try

if ($cat_not_in) {
  $args['category__not_in'] = $cat_not_in;
}
if ($tag_not_in) {
  $args['tag__not_in'] = $tag_not_in;
}

Also see WP Codex - WP_Query it allows for category exclusion by prefixing the category ID with a - (minus). Worth a try too. SO if your building your $cat_not_in array you could just prefix the IDs with - and then

if ($cat_not_in) {
  $args['cat'] = $cat_not_in;
}

Another approach completely might be to get a list of all category IDs into a $cat_get array and then iterate through the $cat_not_in array or string and pop the IDs you don't want off the $cat_get array then you can use the same code as above like this

if ($cat_not_in) {
  $args['cat'] = $cat_get;
}