How to resolve the algorithm One of n lines in a file step by step in the Clojure programming language

Published on 12 May 2024 09:40 PM
#Clojure

How to resolve the algorithm One of n lines in a file step by step in the Clojure programming language

Table of Contents

Problem Statement

A method of choosing a line randomly from a file: Is to:

Note: You may choose a smaller number of repetitions if necessary, but mention this up-front. Note: This is a specific version of a Reservoir Sampling algorithm: https://en.wikipedia.org/wiki/Reservoir_sampling

Let's start with the solution:

Step by Step solution about How to resolve the algorithm One of n lines in a file step by step in the Clojure programming language

Source code in the clojure programming language

(defn rand-seq-elem [sequence]
  (let [f (fn [[k old] new]
            [(inc k) (if (zero? (rand-int k)) new old)])]
    (->> sequence (reduce f [1 nil]) second)))

(defn one-of-n [n]
  (rand-seq-elem (range 1 (inc n))))

(let [countmap (frequencies (repeatedly 1000000 #(one-of-n 10)))]
  (doseq [[n cnt] (sort countmap)]
    (println n cnt)))


1 99350
2 99933
3 99820
4 100266
5 100675
6 100370
7 99842
8 100020
9 100342
10 99382


(require '[clojure.java.io :as io])

(defn rand-line [filename]
  (with-open [reader (io/reader filename)]
    (rand-seq-elem (line-seq reader)))

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