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From Joe Spears <>
Subject Re: Recommending items for anonymous users
Date Mon, 19 Apr 2010 22:00:22 GMT

Responses inline.

Yep, I know what you mean. I didn't really talk about this (yet) in
> the book and likely should spend a page on it.

That would be great. I mean, the two discovery problems are 'user' discovery
and 'item' discovery. Using content-based approaches, I can do something
about when to recommend a new item... but the user approach example would be

Of course, I wouldn't want to talk you out of documenting the best-practice
for Mahout based item discovery in the final version of the book.

> One solution is to punt on the problem, as Ted says: until you get
> enough data or the user has a real presence, don't recommend.

In my case, this isn't practical. For now, (and in my home grown, deprecated
recommender) I have a "backfill list" (built with system-wide stats) that I
use to make a recommendation when I can't come up with anything from my
existing recommender... but the main point of my email was that I may want
to get rid of this and do as much as possible inside of Mahout.

> ...

> I can offer you a mildly hacky but fairly useful middle-ground:
> PlusAnonymousUserDataModel. It decorates/wraps your DataModel and lets
> you temporarily set preferences for one anonymous new user. (You need
> to think of thread-safety potentially -- you can only do this for one
> user at a time.)
This would be ideal. I will be using a default userid of 0 for anonymous
users, and as far as the application is concerned, I can treat all anonymous
users as the same anonymous user for now.



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