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From Claudio Martella <>
Subject about user/item scaling
Date Sat, 27 Feb 2010 18:28:07 GMT

I'm gettin into mahout through the reading of Mahout in action. I'm
pretty curious about this sentence:

[talking about item-based an user-based reccomendation systems]

"They do have notably different properties. For instance, the running
time of an item-based
recommender scales up as the number of items increases, whereas a
user-based recommender’s
running time goes up as the number of users increases.
This suggests one reason that you might choose an item-based
recommender: if the number of users
is relatively low compared to the number of items, the performance
advantage could be significant."

How would the item-based recommender be a good choice with a huge number
of items if the item-based recommender's cost grows with the number of


Claudio Martella
Digital Technologies
Unit Research & Development - Analyst

TIS innovation park
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Fax  +39 0471 068 129

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