grouping posts by categories for FilterWP display

php_snippets.php

<?php

class FWSP_Group_Sub_Cats {
		public static $last_cat;
	
		public static function init() {

			self::$last_cat = false;
			
			add_filter('posts_orderby', array( __CLASS__, 'fwsp_orderby_cat' ), 10, 2);	
			add_action('the_post', array( __CLASS__, 'fwsp_add_cat_seperator' ), 10, 2);
			add_filter( 'get_terms', array( __CLASS__, 'fwsp_filterout_subcats' ), 10, 2 );
		}
	
		/* Ordering by a taxonomy, specifically, when the query is being made for 'post' post type, and is a taxonomy query */
		public static function fwsp_orderby_cat( $orderby_statement, $wp_query ) {
			if ($wp_query->get( 'post_type' ) === 'post' && $wp_query->get( 'tax_query' ) )  {
				$orderby_statement = "wp_term_relationships.term_taxonomy_id ASC, ".$orderby_statement;
			}
			return $orderby_statement;
		}

		/* This function inserts seperators among the grid items, with the category name that the post belongs to. */
		public static function fwsp_add_cat_seperator( $post, $wp_query ) {

			if ($wp_query->get( 'post_type' ) === 'post' && $wp_query->get( 'tax_query' ) )  {
				$terms = get_the_terms( $post, 'category' );

				// assuming, there is only one category
				if( ! empty( $terms[0] ) && ( empty( self::$last_cat ) || self::$last_cat !== $terms[0]->slug ) ) {
					self::$last_cat = $terms[0]->slug;
					echo "<div class='fwsp_cat_seperator'><h3>".$terms[0]->name."</h3></div>";
				}
			}
		}

		public static function fwsp_filterout_subcats( $terms, $taxonomy ) {

			if( count($taxonomy) === 1 && 'category' === $taxonomy[0] ) {
				$terms = array_filter( $terms, function( $term ) {
					return !$term->parent;
				} );
			}

			return $terms;
		}

}

FWSP_Group_Sub_Cats::init();

style.css

	.fwsp_cat_seperator {
	  flex-basis: 100% !important;
	}