Trending patterns

[Mark]

Sorry if this isn't the right place to ask but how would I go about 
finding trending data over a certain period of time.

For example: http://www.ebay.com has a section "Trends on eBay" that is 
updated daily. I was wondering how this can be accomplished using Mahout 
(if possible)

For input I have:
    - user searches by day
    - titles of products purchased by day

Would this require some sort of clustering? classification?

Thanks in advance