Tweaks for ElasticPress's Related Posts Features

elasticpress-related-posts-adjustments.php

<?php
// For Elastisearch docs, see https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-mlt-query.html#mlt-query-term-selection

add_filter(
	'ep_formatted_args',
	function ( $formatted_args, $args ) {
		if ( empty( $args['more_like'] ) ) {
			return $formatted_args;
		}

		if ( ! @isset( $formatted_args['query']['more_like_this'] ) ) {
			return $formatted_args;
		}

		$formatted_args['query']['more_like_this']['min_word_length'] = 4;
		$formatted_args['query']['more_like_this']['stop_words']      = [ 'a', 'an', 'and', 'are', 'as', 'at', 'be', 'but', 'by', 'for', 'if', 'in', 'into', 'is', 'it', 'no', 'not', 'of', 'on', 'or', 'such', 'that', 'the', 'their', 'then', 'there', 'these', 'they', 'this', 'to', 'was', 'will', 'wit' ];

		return $formatted_args;
	},
	20,
	2
);

add_filter(
	'ep_related_posts_fields',
	function( $fields ) {
		$fields = array_merge(
			$fields,
			[ 'post_content_filtered', 'terms.category.name' ]
		);
		return $fields;
	}
);

add_filter(
	'ep_related_posts_min_term_freq',
	function() {
		return 2;
	}
);

add_filter(
	'ep_related_posts_max_query_terms',
	function() {
		return 25;
	}
);

add_filter(
	'ep_find_related_args',
	function( $args ) {
		$args['orderby'] = '_score';
		$args['order']   = 'DESC';

		return $args;
	}
);

add_filter(
	'ep_find_related_args',
	function( $args ) {
		$args['post_type'] = [ 'post', 'page' ];
		return $args;
	}
);