1. Go to your wp-admin (Dashboard), click on Tools -> WP-Table Reloaded, edit your existing table, then insert this following code into your Custom Commands text field in the DataTables JavaScript Features:

   "aoColumns": [ { "sSortDataType": "dom-text" }, { "sSortDataType": "dom-text" }, { "sSortDataType": "dom-text" }, { "sSortDataType": "dom-text" }, { "sSortDataType": "numeric", "sType": "numeric" }]

   From that code above, in order to define the columns, we use aoColumns as the keyword. We can see that from the first until the fourth column has sSortDataType property and the value is dom-text. In the fifth column, both sSortDataType and sType have the value of numeric.

2. Save the changes and reload your table in the front-end of your website.

The important thing that you need to know is when you define a column as the Numeric data type, then you cannot insert another the different data type. In addition, you cannot format the data, for example, by adding the comma or dot character as separator directly to the data.

Here is the steps you have to do:

1. Go to your wp-admin (Dashboard) of your website, and click on the Tools -> WP-Table Reloaded, and then click on the Plugin Options.
2. Make sure you have already checked the “Yes, include and load the following custom CSS commands. This should be used to change the table layout and styling.” item, next to the “Custom CSS:” directive.
3. In the Custom CSS: directive, enter this following code:

   .wp-table-reloaded-id-1 .row-1 .column-1, .row-1 .column-2, .row-1 .column-3, .row-1 .column-4, .row-1 .column-5 { 
         text-align: center; 
   }
   .wp-table-reloaded-id-1 .column-1, .column-4 { 
         text-align: right; 
   }
   .wp-table-reloaded-id-1 .column-3 { 
         text-align: center; 
   }

   From that code above, assuming there is only one table (with table id = 1) that I have created, so you will see that .wp-table-reloaded-id-1 means that this style will be applied to the table which has the table id = 1. If you want to apply it also to another table (for example the table which table id = 2), then simply using .wp-table-reloaded-id-2, and so on.

   Another important thing that you need to know is that if you want to change the table style only for the certain row and column, then you have to write down the .row part must precede the .column, as being shown in the following example:

   .wp-table-reloaded-id-1 .row-1 .column-1, .row-1 .column-2, .row-1 .column-3, .row-1 .column-4, .row-1 .column-5 { 
         text-align: center; 
   }

   But if you want to change the style for the whole column (regardless which row it is), then you don’t need to include the .row, as being shown in the following code:

   .wp-table-reloaded-id-1 .column-1, .column-4 { 
         text-align: right; 
   }
   .wp-table-reloaded-id-1 .column-3 { 
         text-align: center; 
   }

4. Save the changes, and make sure your table has a new style.

Open your /wp-admin/includes/template.php file, and find this code:

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		case 'users':
			$_wp_column_headers[$page] = array(
				'cb' => '<input type="checkbox" />',
				'username' => __('Username'),
				'name' => __('Name'),
				'email' => __('E-mail'),
				'role' => __('Role'),
				'posts' => __('Posts')
			);

then replace with this following code:

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		case 'users':
			$_wp_column_headers[$page] = array(
				'cb' => '<input type="checkbox" />',
				'username' => __('Username'),
				'name' => __('Name'),
				'email' => __('E-mail'),
				'role' => __('Role'),
				'posts' => __('Posts'),
				'user_registered' => __('Registered Date') // added by Masino Sinaga, January 13, 2010
			);

Find again this code:

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			default:
				$r .= "<td $attributes>";
				$r .= apply_filters('manage_users_custom_column', '', $column_name, $user_object->ID);
				$r .= "</td>";
		}

before the first line of that code, please insert this following code:

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			case 'user_registered':  // added by Masino Sinaga, January 13, 2010
				$r .= "<td $attributes>$user_object->user_registered</td>";
				break;

That’s all. Now, go to your wp-admin of your WordPress website, then see the Authors & Users page under the Users menu. You should see now the new column at the right most of the list named Registered Date. I had tested and it worked like a charm.

Please do not hesitate to leave your comment if you have a new idea how to implement this using the plugin in WordPress.

Hopefully this will help someone else out there.

Updated on October 5, 2011: That article above I wrote when the version of WordPress was under 3.0. I found a great plugin today in order to do the same function above. It is Recently Registered.