transpose.clj

(ns transpose
  (:require [clojure.test :refer :all]))

;; Matrix Transpose
;;
;; If you Google the solution, you'll find this:
;;
;; ```clojure
;; (def transpose
;;   (partial apply map vector))
;; ```
;;
;; I struggle to understand that.
;; So I implemented transpose in a way I understand

(defn transpose [m]
  (when (seq (flatten m))
    (cons (map first m)
          (transpose (map rest m)))))

(def input
  [[1 2 3]
   [4 5 6]
   [7 8 9]])

(def expected-output
  [[1 4 7]
   [2 5 8]
   [3 6 9]])

(deftest transpose-test
  (testing "it matches expected output"
    (is (= (transpose input) expected-output)))

  (testing "it works both ways"
    (is (= (transpose expected-output) input))))