Request/GetSearchRecordsByPDC.php
public function selectColumns($columns)
    {
        if (!is_array($columns)) {
            $columns = func_get_args();
        }
        $this->request->setParam(
            'selectColumns',
            $this->request->getModule() . '(' . implode(',', $columns) . ')'
        );
        return $this;
    }
public function selectColumns($columns)
    {
        if (!is_array($columns)) {
            $columns = func_get_args();
        }
        $this->request->setParam(
            'selectColumns',
            $this->request->getModule() . '(' . implode(',', $columns) . ')'
        );
        return $this;
    }
Column names to select i.e, ['Last Name', 'Website', 'Email']
When not set defaults to all columns

@param array|string $columns
@return GetSearchRecordsByPDC