Relabel author names from Login to Last Name, First Name when displaying Co-Authors Pro as a taxonomy in Search & Filter Pro Raw, and sort by the new label

functions.php

// Relabel Co-Authors in Search & Filter

    function filter_function_name($input_object, $sfid) {

        if ($input_object['name'] == '_sft_author') {

		global $coauthors_plus;
			
		// Update option labels before rendering

			foreach($input_object['options'] as $key => $option) {

				// Rename "all items" label - this is always the option with no value

					if($option->value=="") {

						$option->label = "All Authors";

					} else {

						$user = $coauthors_plus->get_coauthor_by( 'user_nicename', $option->value );

						$input_object['options'][$key]->label = $user->last_name . ', ' . $user->first_name . ' ' . ' (' . $option->count . ')';

	    				}

	        	}

	        	// Sort options...

	        		$sortArray = array(); 

	        		foreach($input_object['options'] as $option) { 

				    foreach($option as $key => $value) { 

				        if(!isset($sortArray[$key])) { 

				            $sortArray[$key] = array(); 

				        } 

				        $sortArray[$key][] = $value; 

				    }

				}

				// ...by label

	        		$orderby = "label";

				array_multisort($sortArray[$orderby],SORT_ASC,$input_object['options']); 

	}
		
		// Return

			return $input_object;

	}

	add_filter('sf_input_object_pre', 'filter_function_name', 10, 2);