How to count value column in Apache Pig while filter out distinct key

Question

I'm trying to count the total number of ordered prouduct(the quantity) by product_id.

The data looks like this.

(product_id, quantity)

which also is

(11, 5)
(11, 2)
(11, 1)
(12, 9)
(12, 1)
(13, 5)
(13, 9)
(13, 9)

There will be a duplicated product_id as it has been ordered many times and each time with various quantity.

How do I count the total quantity per product_id?

Expected out come will be

(11, 8)
(12, 10)
(13, 23)

Answer 1

You can use GROUP BY.

Lets say you have your expected input data in a variable called products.

count_prod = FOREACH (GROUP products BY product_id) {
get_one_record = LIMIT product 1;
GENERATE FLATTEN(get_one_record), SUM(quantity) AS total_quantity;
}; 
final_products_data = FOREACH count_prod GENERATE get_one_record::product_id AS product_id, total_quantity;

Hope this helps.