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(ns clj-slope-one.core
(use clj-slope-one.utils))
(defn train [data]
(let [item-pair-diffs (flatten-initial
(for [[user preferences] data]
(for [[i u_i] preferences
[j u_j] preferences
:when (and (not= i j) u_i u_j)]
[[i j] (- u_i u_j)])))
[freqs diffs] (reduce (fn [[freqs-so-far diffs-so-far] [item-pair diff]]
[(update-in freqs-so-far item-pair (fnil inc 0))
(update-in diffs-so-far item-pair (fnil + 0) diff)])
[{} {}]
{:freqs freqs
:differences (map-nested-vals (fn [item-pair diff] (/ diff (get-in freqs item-pair))) diffs)}))
(defn known-items [model]
(-> model :differences keys))
(defn predict [{:keys [differences freqs] :as model} preferences item]
(apply /
(reduce (fn [[num denom] [i rating]]
(let [freqs_ji (get-in freqs [item i])]
[(+ num (* (+ (get-in differences [item i]) rating) freqs_ji))
(+ denom freqs_ji)]))
[0 0]
(filter #(not= (first %) item) preferences))))
(defn predictions
([model preferences]
(predictions model preferences (filter #(not (contains? preferences %)) (known-items model))))
([model preferences items]
(mapmap (partial predict model preferences) items)))
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