Snippet to retrieve filtered values from a specific Formidable form and populate a dropdown

populate_formidable_drop_down.php

<?php

add_filter( frm_setup_new_fields_vars, frm_populate_classes, 20, 2 );
add_filter( frm_setup_edit_fields_vars, frm_populate_classes, 20, 2 ); //use this function on edit too

function frm_populate_classes( $values, $field ){
    global $wpdb;
    $prefix = $wpdb->prefix;
    $frm_items = $prefix . 'frm_items';
    $frm_item_metas = $prefix . 'frm_item_metas';

    if( $field->id == '203' ) {

	    $sql = "SELECT t1.meta_value FROM `{$frm_item_metas}` t1 LEFT JOIN `{$frm_items}` t2 ON t1.item_id = t2.id LEFT JOIN `{$frm_item_metas}` t3 ON t1.item_id = t3.item_id WHERE t1.field_id = '152' AND t2.form_id = '15' AND t3.field_id = '153' AND t3.meta_value = 'Class' ORDER BY t1.meta_value";

        //the Query
		$dataset = $wpdb->get_results( $sql, ARRAY_A );
      
        unset($values['options']); //break the binding of any existing content in the values array

        $values['options'][]="";

        //the Loop
        if(! empty($dataset)){
            foreach( $dataset as $class ){
            	$values['options'][] = $class['meta_value'];
            }
        }
    }
	return $values;
}