Cash cart with session

Use session to implement shopping cart and use session to implement shopping cart. I want to insert the information of a commodity into the $ arr array as an array, and the last array is a two-dimensional array, store all the purchased information, so if the product has been purchased, how can I determine and only increase its pdnum by 1 without inserting a new item? this code group uses session to implement the shopping cart.
Use session to implement the shopping cart. I want to insert the information of a commodity into the $ arr array as an array if I click to add it to the shopping cart,
Finally, this array is a two-dimensional array that stores all purchased information,
So if the product has already been purchased, how can I determine and just increase its pdnum by 1 without inserting a new item,
This code cannot be organized. who can help ..
$ Arr = array ("pdname" => "xx", "pdprice" => 12, "pdnum" => 1 ), array ("pdname" => "yy", "pdprice" => 22, "pdnum" => 1 ))
?>
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Why do we need a two-dimensional array?
Isn't it easier to use a one-dimensional model?
Commodity name (or commodity) => quantity