This example will allow you to execute different actions on the data according to the type of field.

add_filter( 'frm_api_prepare_data', 'prepare_data' );
function prepare_data( $data, $fields ) {
    foreach ( $fields as $k => $field ) {
        switch ( $field->type ) {
            case 'checkbox':
            case 'select':
                //do something
            break;
            case 'file':
                //do something
            break;
            case 'date':
                FrmAPIAppHelper::format_date( $field, $data['item_meta'][ $field->id ] );
        }
    }

    return $data;
}