productName	dollar_sales
1937 Lincoln Berline	3,726
1936 Mercedes-Benz 500K Special Roadster	1,768
1952 Alpine Renault 1300	5,572
1962 LanciaA Delta 16V	5,026
1958 Setra Bus	3,284
1940 Ford Pickup Truck	3,308
1926 Ford Fire Engine	1,283
1913 Ford Model T Speedster	2,489
1934 Ford V8 Coupe	2,164
18th Century Vintage Horse Carriage	2,173

->pipe(new Map([
    '{value}' => function($row, $meta, $index, $mapState) {
        $numTopRows = 2;
        //If a row is among the first 2 rows
        if ($index < $numTopRows) {
            $mappedRows = [$row];
            //return it to send to next process or datastore
            return ['{rows}' => $mappedRows]; 
        }
        //Otherwise,
        //initialise a key of this Map's state to use for sum
        $sum = Util::init($mapState, 'sumOthers', []);
        foreach ($row as $columnName => $value) {
            Util::init($sum, $columnName, 0);
            //if column name = 'dollar_sales', sum it
            $sum[$columnName] = $columnName === 'dollar_sales' ? 
                $sum[$columnName] + $value : 'Other Customers';
        }
        //Save the sum to this Map's state
        $mapState['sumOthers'] = $sum;
        $mappedRows = [];
        //Skip rows after the first 2 rows (they won't be sent to next process or datastore) 
        //return this Map's state to save it
        return ['{rows}' => $mappedRows, '{state}' => $mapState];
        
    },
    '{end}' => function($count, $mapState) {
        //After all rows had been sent
        //retrieve this Map's state and send it at the end of Map process
        $rowsToSend = [$mapState['sumOthers']];
        return $rowsToSend;
    },
]))