Let price be a PyTorch tensor with shape (num_days, num_products).
Let purchased_product_by_day be an integer tensor with shape (num_days,), with values in range(num_products).
Intuitively, price lists the price, for each day, of each product, and purchased_product_by_day are the indices of purchased products, one per day.
To obtain a tensor containing the expense per day, I can write
price[list(range(num_days)), purchased_product_by_day]
but this iterates over days at the Python level. I would like to obtain the same tensor on the C level.
I tried
price[:, purchased_product_by_day]
but that does not work, being equivalent to indexing each row by purchased_product_by_day for each day and stacking the results.
Is there a way to do that without iteration at the Python level?
