show more columns: author, date and last edit: and and a new filter: Author:

admin_cols_filters.php

<?php

/**
 * *******
 * Interactive Geo Maps user filter
 * ********************************
 */

add_filter( 'manage_igmap_posts_columns', 'igmaps_cols', 11 );
function igmaps_cols( $columns ) {
	$columns['author']      = 'Author';
	$columns['date']        = 'Date';
	$columns['last_edited'] = 'Last Edited';
	return $columns;
}


// Display the content of the Last Edited column
function display_last_edited_column_content( $column, $post_id ) {
	// Display the last edited date for the post
	if ( $column == 'last_edited' ) {
		$last_edited = get_the_modified_date( 'Y-m-d H:i:s', $post_id );
		echo $last_edited;
	}
}
add_action( 'manage_igmap_posts_custom_column', 'display_last_edited_column_content', 10, 2 );


// Make the Last Edited column sortable
function make_last_edited_column_sortable( $sortable_columns ) {
	$sortable_columns['last_edited'] = 'last_edited';
	return $sortable_columns;
}
add_filter( 'manage_edit-igmap_sortable_columns', 'make_last_edited_column_sortable' );


// Add the filter dropdown to the 'igmap' custom post type
function add_author_filter_to_igmap_list() {
	global $typenow;

	// Ensure we're on the 'igmap' custom post type
	if ( $typenow === 'igmap' ) {

		// Get all posts of the specified Custom Post Type
		$args = array(
			'post_type'        => 'igmap',
			'posts_per_page'   => 500,
			'fields'           => 'all',
			'suppress_filters' => true, // Ignore pre_get_posts hooks
		);

		$cpt_entries = new WP_Query( $args );

		// If there are posts, retrieve the unique authors
		$authors = [];
		if ( $cpt_entries->have_posts() ) {
			foreach ( $cpt_entries->posts as $post_entry ) {
				$author_id = $post_entry->post_author;
				if ( ! empty( $authors[ $author_id ] ) ) {
					++$authors[ $author_id ]->igmaps_count;
					continue;
				}
				$authors[ $author_id ] = get_userdata( $author_id );

				$authors[ $author_id ]->igmaps_count = 1;

			}
		}

		if ( ! empty( $authors ) ) {
			echo '<select name="igmap_author_filter">';
			echo '<option value="">Filter by Author</option>';

			foreach ( $authors as $author ) {
				$selected = isset( $_GET['igmap_author_filter'] ) && $_GET['igmap_author_filter'] == $author->ID ? 'selected' : '';
				echo '<option value="' . $author->ID . '" ' . $selected . '>' . $author->display_name . ' ( ' . $author->data->igmaps_count . ' ) </option>';
			}

			echo '</select>';
		}
	}
}
add_action( 'restrict_manage_posts', 'add_author_filter_to_igmap_list', 999 );

// Modify the query based on the selected author filter
function filter_igmap_by_author( $query ) {
	global $pagenow;

	// Ensure we're on the 'edit.php' page and dealing with the 'igmap' custom post type
	if ( is_admin() && $pagenow == 'edit.php' && isset( $_GET['post_type'] ) && $_GET['post_type'] == 'igmap' && isset( $_GET['igmap_author_filter'] ) ) {
		$query->query_vars['author'] = $_GET['igmap_author_filter'];
	}
}
add_filter( 'parse_query', 'filter_igmap_by_author' );