equal-weight mapped counter

map_counter.clj

(comment
;; "Usage Example"
(facts
  (attrib-model [["a" "a"]
                 ["b"]
                 ["b" "c" "a"]
                 ["b"]]
                equal-weights) => {"a" 4/3, "b" 7/3, "c" 1/3})
)

(defn count-occur [coll]
  (reduce (fn [m x] 
            (assoc m x (inc (m x 0)))) 
          {} coll))

(defn map-entry? [x]
  (= (type x) clojure.lang.MapEntry))

(defn equal-weights 
"
  Returns a map with the keys being the elements of an input collection 
  and vals as a ratio of occurence within the input collection.

  Example:
  => (equal-weights [\"a\" \"a\" \"b\" \"c\"]) 
  {\"a\" 2/4, \"b\" 1/4, \"c\" 1/4}
"  
  [coll]
  (let [cnt  (count-occur coll)
        sum  (apply + (vals cnt))]
    (loop [m-out {}, m-in cnt]
      (let [e  (first m-in)]
        (if (map-entry? e)
          (recur (assoc m-out (key e) (/ (val e) sum)) (rest m-in))
          m-out)))))

(defn update-map [m e]
  (if-let [[k v] e]
    (assoc m k (+ (m k 0) v))
    m))

(defn aggregate-maps [m1 m2]
  (let [e  (first m2)]
    (if (map-entry? e)
      (aggregate-maps (update-map m1 e) (rest m2))
      m1)))

(defn attrib-model [coll model]
  (let [cnts  (map model coll)]
    (reduce aggregate-maps {} cnts)))