Group SearchWP results by Source, sort by relevance within each Source group

searchwp-customizations.php

<?php

// Group SearchWP results by Source, sort by relevance within each Source group.
add_filter( 'searchwp\query\mods', function( $mods, $query ) {
	$mod = new \SearchWP\Mod();
	$mod->order_by( function( $mod ) {
		// Search results should be grouped by Sources in this order.
		// NOTE: _ALL_ Engine Sources must be included here!
		$source_order = [
			'user',
			\SearchWP\Utils::get_post_type_source_name( 'post' ),
			\SearchWP\Utils::get_post_type_source_name( 'page' ),
		];

		return "FIELD({$mod->get_foreign_alias()}.source, "
			. implode( ',', array_filter( array_map( function( $source_name ) {
				global $wpdb;

				return $wpdb->prepare( '%s', $source_name );
			}, $source_order ) ) ) . ')';
	}, '', 1 );

	$mods[] = $mod;

	return $mods;
}, 10, 2 );

This seems to be throwing an error with the latest release
substr() expects parameter 1 to be string, object given

I really appreciate these snippets, they've helped immensely with the project I'm currently working on.

Is it possible to set a limit to the number of results returned per source? (eg. 5 results per source.)

Thanks in advance!