dynamic time warping

dynamic_time_warping.clj

(ns dtw.core)
 
(defn distance [a b]
  (Math/Pow (- a b) 2))
 
(defn dtw [s t]
  (let [n (count s)
        m (count t)
        bottom (apply hash-map
                 (mapcat (fn [i] [[i 0] Double/PositiveInfinity])
                   (range 1 n)))
        left (apply hash-map
               (mapcat (fn [i] [[0 i] Double/PositiveInfinity])
                 (range 1 m)))
        d (merge {[0 0] 0} bottom left)] 
    ((reduce
       (fn [acc [i j]]
         (assoc acc
           [i j]
           (+ (distance (nth s i) (nth t j))
             (min
               (acc [(dec i) j])
               (acc [i (dec j)])
               (acc [(dec i) (dec j)])))))
       d
       (for [i (range 1 n)
             j (range 1 m)]
         [i j]))
     [(dec n) (dec m)])))

adapted from https://gist.github.com/nasser/a11a27e0e28538bc573e