A computer-implemented service recommends items to a user based on items
previously selected by the user, such as items previously purchased,
viewed, or placed in an electronic shopping cart by the user. The items
may, for example, be products represented within a database of an online
merchant. In one embodiment, the service generates the recommendations
using a previously generated table that maps items to respective lists of
"similar" items. To generate the table, historical data indicative of
users' affinities for particular items is processed periodically to
identify correlations between item interests of users (e.g., items A and
B are similar because a large portion of those who selected A also
selected B). Personal recommendations are generated by accessing the
table to identify items similar to those selected by the user. In one
embodiment, items are recommended based on the current contents of a
user's shopping cart.