public function aggregateNumericMetrics($columns, $operationToApply = false)
    {
        $metrics = $this->getAggregatedNumericMetrics($columns, $operationToApply);

        foreach ($metrics as $column => $value) {
            $value = Common::forceDotAsSeparatorForDecimalPoint($value);
            $this->archiveWriter->insertRecord($column, $value);
        }
        // if asked for only one field to sum
        if (count($metrics) == 1) {
            return reset($metrics);
        }

        // returns the array of records once summed
        return $metrics;
    }