С помощью приведенного ниже кода вы можете получить ожидаемый результат.
<?php
$array = Array
( Array
(
"iProduct_id" => "1",
"fTotal_qty" => "200",
),
Array
(
"iProduct_id" => "2",
"fTotal_qty" => "400",
),
Array
(
"iProduct_id" => "6",
"fTotal_qty" => "500",
),
Array
(
"iProduct_id" => "4",
"fTotal_qty" => "300",
),
Array
(
"iProduct_id" => "5",
"fTotal_qty" => "200",
),
Array
(
"iProduct_id" => "6",
"fTotal_qty" => "200",
),
Array
(
"iProduct_id" => "1",
"fTotal_qty" => "300",
)
);
$resultArray = array();
foreach($array as $key => $value){
if(array_key_exists($value['iProduct_id'], $resultArray)){
$resultArray[$value['iProduct_id']]['total_qty'] = $resultArray[$value['iProduct_id']]['total_qty'] + $value['fTotal_qty'];
}else {
$resultArray[$value['iProduct_id']]['product_id'] = $value['iProduct_id'];
$resultArray[$value['iProduct_id']]['total_qty'] = $value['fTotal_qty'];
}
}