Reputation: 40969
I'm doing some exploratory work on recommendation systems and have been reading about collaborative filtering techniques involving user-based, item-based, and SVD algorithms. I am also trying out R's recommenderlab package.
One apparent assumption in the literature is that the user data has labelled items based on a rating scale, e.g. between 1 and 5 stars. I'm looking at problems where the user data does not have ratings but rather just transactions. For example, if I want to recommend restaurants to a user, the only data I have is how often he has visited other restaurants.
How can I convert these "transaction" counts into ratings that can be used by recommendation algorithms that expect a fixed-scale rating? One approach I thought of is simple binning:
0 stars = 0-1 visits
1 star = 2-3 visits
...
5 stars = 10+ visits
However, that doesn't seem like it would work well. For example, if someone visited a restaurant only once, he may still really love it.
Any help would be appreciated.
Upvotes: 0
Views: 1397
Reputation: 7394
Here's an idea: restaurants the user has visited zero or one times tell you nothing about what they like. Restaurants they have visited many times tell you lots. Why not just look for restaurants similar to those the customer most regularly frequents? In this way, you're using positive information (what they like) but none of the negative since you don't have access to it anyway.
If you absolutely had to infer some continuous measure, I think it would only be sensible to look at the propensity for another visit given past behaviour. This would start with the prior probability of choosing that restaurant (background frequency, or just uniform over restaurants) with a likelihood term related to the number of visits to that restaurant. In this way the more a user visits a restaurant the more likely they are to visit again.
Upvotes: 0
Reputation: 1395
I would try different approaches. As you said, only visited once may indicate that the user still loves the restaurant but you don't know for sure. Your goal is not to optimize for one single user rather for all users. So for this, you can split your data into training and test data. Train on the training data with different scales and test on the test data.
The different scales may be
a binary scale (0:never visited, 1: visited). This is mostly used in online shops (bought or not). Would support your assuption with the one time visit.
your presented scale or other ranges for the 5 stars. You can also use more than 5 stars. I would potentially not group 0-1 visits.
The approach with the best accuracy should be chosen.
Upvotes: 1