transpose.js

/*
 *  Matrix Transpose
 *
 *  As a Ramda user, I'm aware the library already has a `transpose` function.
 *  Still, I believe it is a fun exercise.
 *
 */

const { all, isEmpty, map, head, tail, concat } = require("ramda");

const transpose = (m) =>
  all(isEmpty, m)
    ? []
    : concat(Array(map(head, m)), transpose(map(tail, m)));

describe("transpose", () => {
  const sampleInput = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
  ];

  const expectedOutput = [
    [1, 4, 7],
    [2, 5, 8],
    [3, 6, 9]
  ];

  test("transpose a square matrix", () => {
    expect(transpose(sampleInput)).toEqual(expectedOutput);
  });

  test("transpose a square matrix back", () => {
    expect(transpose(transpose(sampleInput))).toEqual(sampleInput);
  });
});