Add last modified to WordPress admin for page and post listings

last-modified.php

/** Andrew Norcross - Date Modified Display - http://andrewnorcross.com/tutorials/modified-date-display/ */
// Post Columns
add_action ( 'manage_posts_custom_column',	'rkv_post_columns_data',	10,	2	);
add_filter ( 'manage_edit-post_columns',	'rkv_post_columns_display'			);
function rkv_post_columns_data( $column, $post_id ) {
	switch ( $column ) {
	case 'modified':
		$m_orig		= get_post_field( 'post_modified', $post_id, 'raw' );
		$m_stamp	= strtotime( $m_orig );
		$modified	= date('n/j/y @ g:i a', $m_stamp );
	       	$modr_id	= get_post_meta( $post_id, '_edit_last', true );
	       	$auth_id	= get_post_field( 'post_author', $post_id, 'raw' );
	       	$user_id	= !empty( $modr_id ) ? $modr_id : $auth_id;
	       	$user_info	= get_userdata( $user_id );
	
	       	echo '<p class="mod-date">';
	       	echo '<em>'.$modified.'</em><br />';
	       	echo 'by <strong>'.$user_info->display_name.'<strong>';
	       	echo '</p>';
		break;
	// end all case breaks
	}
}
function rkv_post_columns_display( $columns ) {
	$columns['modified']	= 'Last Modified';
	return $columns;
}

// Page Columns
add_action ( 'manage_pages_custom_column',	'rkv_heirch_columns',	10,	2	);
add_filter ( 'manage_edit-page_columns',	'rkv_page_columns'				);
function rkv_heirch_columns( $column, $post_id ) {
	switch ( $column ) {
	case 'modified':
		$m_orig		= get_post_field( 'post_modified', $post_id, 'raw' );
		$m_stamp	= strtotime( $m_orig );
		$modified	= date('n/j/y @ g:i a', $m_stamp );
	       	$modr_id	= get_post_meta( $post_id, '_edit_last', true );
	       	$auth_id	= get_post_field( 'post_author', $post_id, 'raw' );
	       	$user_id	= !empty( $modr_id ) ? $modr_id : $auth_id;
	       	$user_info	= get_userdata( $user_id );
	
	       	echo '<p class="mod-date">';
	       	echo '<em>'.$modified.'</em><br />';
	       	echo 'by <strong>'.$user_info->display_name.'<strong>';
	       	echo '</p>';
		break;
	// end all case breaks
	}
}
function rkv_page_columns( $columns ) {
	$columns['modified']	= 'Last Modified';
	return $columns;
}

// Do the sort!
function last_modified_column_register_sortable( $columns ) {
	$columns["modified"] = "last_modified";
        return $columns;
}
add_filter( "manage_edit-post_sortable_columns", "last_modified_column_register_sortable" );
add_filter( "manage_edit-page_sortable_columns", "last_modified_column_register_sortable" );