Hi:
In paper "Item-Based Top-N Recommendation 
Algorithms"(https://stuyresearch.googlecode.com/hg/blake/resources/10.1.1.102.4451.pdf),
 there are two parameters measuring the quality of recommendation: HR and ARHR.
If I use ALS(Implicit) for top-N recommendation system, I want to check it's 
quality. ARHR and HR are two good quality measures.
I want to contribute them to spark MLlib.  So I want to know whether this is 
meaningful?


(1) If n is the total number of customers/users,  the hit-rate of the 
recommendation algorithm was computed as
hit-rate (HR) = Number of hits / n

(2)If h is the number of hits that occurred at positions p1, p2, . . . , ph 
within the top-N lists (i.e., 1 ≤ pi ≤ N), then the average reciprocal hit-rank 
is equal to:
[cid:image001.png@01CFC086.8EE1FF40]i
.

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