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lujanfernaud's solution

to Matrix in the Ruby Track

Published at Mar 16 2019 · 2 comments
Test suite


This exercise has changed since this solution was written.

Given a string representing a matrix of numbers, return the rows and columns of that matrix.

So given a string with embedded newlines like:

9 8 7
5 3 2
6 6 7

representing this matrix:

    0  1  2
0 | 9  8  7
1 | 5  3  2
2 | 6  6  7

your code should be able to spit out:

  • A list of the rows, reading each row left-to-right while moving top-to-bottom across the rows,
  • A list of the columns, reading each column top-to-bottom while moving from left-to-right.

The rows for our example matrix:

  • 9, 8, 7
  • 5, 3, 2
  • 6, 6, 7

And its columns:

  • 9, 5, 6
  • 8, 3, 6
  • 7, 2, 7

For installation and learning resources, refer to the Ruby resources page.

For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:

gem install minitest

If you would like color output, you can require 'minitest/pride' in the test file, or note the alternative instruction, below, for running the test file.

Run the tests from the exercise directory using the following command:

ruby matrix_test.rb

To include color from the command line:

ruby -r minitest/pride matrix_test.rb


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Submitting Incomplete Solutions

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require 'minitest/autorun'
require_relative 'matrix'

class MatrixTest < Minitest::Test
  def test_extract_a_row
    matrix = Matrix.new("1 2\n10 20")
    assert_equal [1, 2], matrix.rows[0]

  def test_extract_same_row_again
    matrix = Matrix.new("9 7\n8 6")
    assert_equal [9, 7], matrix.rows[0]

  def test_extract_other_row
    matrix = Matrix.new("9 8 7\n19 18 17")
    assert_equal [19, 18, 17], matrix.rows[1]

  def test_extract_other_row_again
    matrix = Matrix.new("1 4 9\n16 25 36")
    assert_equal [16, 25, 36], matrix.rows[1]

  def test_extract_a_column
    matrix = Matrix.new("1 2 3\n4 5 6\n7 8 9\n 8 7 6")
    assert_equal [1, 4, 7, 8], matrix.columns[0]

  def test_extract_another_column
    matrix = Matrix.new("89 1903 3\n18 3 1\n9 4 800")
    assert_equal [1903, 3, 4], matrix.columns[1]
class Matrix
  def initialize(matrix)
    @matrix = matrix

  def rows
    @rows ||= @matrix.each_line.map { |item| item.split.map(&:to_i) }

  def columns

Community comments

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Avatar of sten1ee

Thanks to this solution I realised I've missed doing better, namely - to calculate @rows lazily, on first invocation (@rows ||= ...) Just one note -- you can optimise columns method the same way: @colums ||= row.transpose

Avatar of lujanfernaud

Thanks for your comment.

I didn't memoize #columns thinking that it's not called a second time in this class. But actually, being a public method, it may make sense to also do it.

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