Make a CDF (cumulative distribution function) from a seq of numbers in Clojure

make_cdf.clj

(defn make-cdf
  "Given a seq of numbers, return a plottable vector of [x,y] pairs
  representing the cumulative distribution function.
  Ex:
    (cdf-data [1 2 1 3])
    ; => [[1 0] [1 1/2] [2 3/4] [3 1]]"
  [xs]
  {:pre [(sequential? xs)]}
  (let [n (count xs)
        uniq-xs (->> xs frequencies (into (sorted-map)))
        cdf-xs (keys uniq-xs)
        n-so-far-seq (reductions + (vals uniq-xs))
        cdf-ys (map #(/ % n) n-so-far-seq)
        cdf-xy-pairs (map vector cdf-xs cdf-ys)
        init-pair [(-> uniq-xs first key) 0]]
    (vec (cons init-pair cdf-xy-pairs))))

;; The MIT License (MIT)
;; Copyright (c) 2016 Jeff Terrell
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