Prepare data : many products per row 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.
I my opinion, the best way is if you  create a column for every(!) product. Yes, u will  get a high dimensional sparse Matrix but it should solve you problem quickly.