Rank Score extends the recall metric to take the positions of correct items in a ranked list into account.
rankScore(recommendedIDX, testSetIDX, alpha)indices of the recommended items. Object of class numeric.
indices of the items in the test set. Object of class numeric
is the ranking half life. Object of class numeric.
Rank Score is defined as the ratio of the Rank Score of the correct items to best theoretical Rank Score achievable for the user: $$ rankscore_{p} =\sum_{i\in{h}} 2^{-\frac{rank(i)-1}{\alpha}} $$ $$ rankscore_{max} = \sum_{i=1}^{|T|} 2^{-\frac{i-1}{\alpha}} $$ $$ rankscore = \frac{rankscore_p}{rankscore_{max}} $$