lujanfernaud's solution to Matrix on the Ruby track

Instructions

Test suite

Solution

Note:

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

Source

Warmup to the saddle-points warmup. http://jumpstartlab.com

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

matrix_test.rb

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]
  end

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

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

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

  def test_extract_a_column
    skip
    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]
  end

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

class Matrix
  def initialize(matrix)
    @matrix = matrix
  end

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

  def columns
    rows.transpose
  end
end

Community comments

Find this solution interesting? Ask the author a question to learn more.

sten1ee

commented almost 2 years ago

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

What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

What compromises have been made?
Are there new concepts here that you could read more about to improve your understanding?

lujanfernaud's solution

to Matrix in the Ruby Track