percentile.clj

(defn compute-percentile
  ; This function compute a percentile over a sequence of numbers.
  [percentile coll]
  {:pre [(number? percentile) (> percentile 0) (< percentile 1) (not (empty? coll))]}
  (let [sorted (sort coll)
        length (count coll)
        index (* percentile length)]
    (if (== (int index) index)
      (let [first (nth sorted (- index 1))
            second (nth sorted index)]
        (/ (+ first second) 2))
      (nth sorted (- (Math/ceil index) 1)))))