wxr_authors_list()

wxr_authors_list( int[] $post_ids = null )

function wxr_authors_list( ?array $post_ids = null ) {
	global $wpdb;

	if ( ! empty( $post_ids ) ) {
		$post_ids       = array_map( 'absint', $post_ids );
		$post_id_chunks = array_chunk( $post_ids, 20 );
	} else {
		$post_id_chunks = array( array() );
	}

	$authors = array();

	foreach ( $post_id_chunks as $next_posts ) {
		$and = ! empty( $next_posts ) ? 'AND ID IN (' . implode( ', ', $next_posts ) . ')' : '';

		$results = $wpdb->get_results( "SELECT DISTINCT post_author FROM $wpdb->posts WHERE post_status != 'auto-draft' $and" );

		foreach ( (array) $results as $result ) {
			$authors[] = get_userdata( $result->post_author );
		}
	}

	$authors = array_filter( $authors );
	$authors = array_unique( $authors, SORT_REGULAR ); // Remove duplicate authors.

	foreach ( $authors as $author ) {
		echo "\t<wp:author>";
		echo '<wp:author_id>' . (int) $author->ID . '</wp:author_id>';
		echo '<wp:author_login>' . wxr_cdata( $author->user_login ) . '</wp:author_login>';
		echo '<wp:author_email>' . wxr_cdata( $author->user_email ) . '</wp:author_email>';
		echo '<wp:author_display_name>' . wxr_cdata( $author->display_name ) . '</wp:author_display_name>';
		echo '<wp:author_first_name>' . wxr_cdata( $author->first_name ) . '</wp:author_first_name>';
		echo '<wp:author_last_name>' . wxr_cdata( $author->last_name ) . '</wp:author_last_name>';
		echo "</wp:author>\n";
	}
}