Java streams grouping a column and fetching multiple aggregated values

Question

If I have a list of object say products, that are to be grouped by product type. And I need the aggregated price and quantity.

{{name:a1,type:normal,price:23,quantity:4}, 
{name:a2,type:normal,price:3,quantity:3},
{name:a3,type:luxury,price:233,quantity:1},
{name:a4,type:luxury,price:123,quantity:2}}

I need a resultant list which looks like this

{{type:normal,price:26,quantity:7},{type:luxury,price:356,quantity:3}}

Is there a way to achieve this using java streams??

[very close was asked yesterday](https://stackoverflow.com/a/52465144/1059372) — Eugene, Sep 24 '18 at 12:59
I need to group by on one column. So should I set name as empty string in reduce and maintain the same type of object as list? How can it be done, if that's the case? — HareshKannan, Sep 24 '18 at 13:11
So do you have a list of maps? A list of products? A list of String? Please clarify. — fps, Sep 24 '18 at 20:19

score 1 · Accepted Answer · answered Sep 24 '18 at 15:16

How about this,

Map<String, Product> result = products.stream()
    .collect(Collectors.groupingBy(Product::getType,
        Collectors.reducing(new Product(null, null, 0, 0), (p1, p2) -> new Product(null, p1.getType(),
            p1.getPrice() + p2.getPrice(), p1.getQuantity() + p2.getQuantity()))));

where Product class should look something like this.

public class Product {
    private String name;
    private String type;
    private double price;
    private int quantity;

    public Product(String name, String type, double price, int quantity) {
        super();
        this.name = name;
        this.type = type;
        this.price = price;
        this.quantity = quantity;
    }
    // ...
}

Works fine for my case. Thanks a lot. – HareshKannan Sep 25 '18 at 07:38 — HareshKannan, Sep 25 '18 at 07:38

Java streams grouping a column and fetching multiple aggregated values

1 Answers1