Prepare data : many products per row

Question

I would like to find how to change my data structure to make it compatible with a ML model, with the following constraints :

• A Product is defined by {id, price, continuousVariable1, ..., continuousVariable10}
• The training set is train.csv. Each line contains a date, a Product, and a list of Products (competing products)
• For each row of train.csv, the size of the list of Products may change.

It would be easy if I had only one competing products : I could put all columns in the same file. But I have many competing products. The output variable is the product price.