The onCSVOutput handler is called when LiveWhale exports a CSV, allowing you to filter or customize it however you like. The example module below adds a new custom column to an exported CSV of event registrations.

<?php
     $_LW->REGISTERED_APPS['my_app']=[
       'title'=>'My App',
       'handlers'=>['onValidateUpload'],
    ];

    class LiveWhaleApplicationMyApp {

      public function onCSVOutput($data_type, $rows) { // formats CSV output
        global $_LW;

        if ($data_type=='event_registrations') { // if these are event RSVPs
          foreach($rows as $key=>$val) {
            if ($key===0) { // add custom column to the header row
              $rows[$key][]='Appointment Time';
              $custom_column_key=sizeof($rows[$key])-1;
            }
            else { // add custom value to each row, in that column
              $custom_value = ''; // you could run a db query, load custom values, or make a calculation based on other column values
              $rows[$key][$custom_column_key]=$custom_value; // add the value to this row
            };
          };
        };

        return $rows;
      }

   }
?>