Comments on: Linear Interpolation and sorted-map http://clj-me.cgrand.net/2009/06/08/linear-interpolation-and-sorted-map/ When the pupil is ready to learn, a teacher will appear. Tue, 07 Sep 2010 05:36:26 +0200 http://wordpress.org/?v=2.9.2 hourly 1 By: Christophe Grand http://clj-me.cgrand.net/2009/06/08/linear-interpolation-and-sorted-map/comment-page-1/#comment-38 Christophe Grand Sun, 20 Sep 2009 09:48:56 +0000 http://clj-me.cgrand.net/2009/06/08/linear-interpolation-and-sorted-map/#comment-38 @john, true, here is an amended version:<br />(defn interpolator <br /> "Takes a coll of 2D points (vectors) and returns <br />  their linear interpolation function."<br /> [points]<br />  (let [m (into (sorted-map) points)]<br />    (fn [x]<br />      (let [[[x1 y1]] (rsubseq m <= x)<br />            [[x2 y2]] (subseq m > x)]<br />        (cond<br />          (not x2) y1<br />          (not x1) y2<br />          :else (+ y1 (* (- x x1) (/ (- y2 y1) (- x2 x1)))))))))<br /><br />;; => (map (interpolator [[0 0] [1 1] [3 2] [4 3]]) (range -1 11/2 1/2))<br />;; (0 0 0 1/2 1 5/4 3/2 7/4 2 5/2 3 3 3) @john, true, here is an amended version:
(defn interpolator
 "Takes a coll of 2D points (vectors) and returns
  their linear interpolation function."
 [points]
  (let [m (into (sorted-map) points)]
    (fn [x]
      (let [[[x1 y1]] (rsubseq m <= x)
            [[x2 y2]] (subseq m > x)]
        (cond
          (not x2) y1
          (not x1) y2
          :else (+ y1 (* (- x x1) (/ (- y2 y1) (- x2 x1)))))))))

;; => (map (interpolator [[0 0] [1 1] [3 2] [4 3]]) (range -1 11/2 1/2))
;; (0 0 0 1/2 1 5/4 3/2 7/4 2 5/2 3 3 3)

]]> By: John http://clj-me.cgrand.net/2009/06/08/linear-interpolation-and-sorted-map/comment-page-1/#comment-37 John Sat, 19 Sep 2009 12:35:47 +0000 http://clj-me.cgrand.net/2009/06/08/linear-interpolation-and-sorted-map/#comment-37 Nice.<br />The function does something sensible for inputs that outside the range of points.<br />(map (interpolator points) (range 0 19/2 1/2))<br />; (0 1/2 1 5/4 3/2 7/4 2 5/2 3 3 3 3 3 3 3 3 3 3 3)<br /><br />But only on one side<br />(map (interpolator points) (range -1 19/2 1/2)) ; java.lang.NullPointerException Nice.
The function does something sensible for inputs that outside the range of points.
(map (interpolator points) (range 0 19/2 1/2))
; (0 1/2 1 5/4 3/2 7/4 2 5/2 3 3 3 3 3 3 3 3 3 3 3)

But only on one side
(map (interpolator points) (range -1 19/2 1/2)) ; java.lang.NullPointerException

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