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RiccardoBoettcher's solution

to ETL in the Ruby Track

Published at Jul 29 2020 · 0 comments
Test suite

We are going to do the Transform step of an Extract-Transform-Load.


Extract-Transform-Load (ETL) is a fancy way of saying, "We have some crufty, legacy data over in this system, and now we need it in this shiny new system over here, so we're going to migrate this."

(Typically, this is followed by, "We're only going to need to run this once." That's then typically followed by much forehead slapping and moaning about how stupid we could possibly be.)

The goal

We're going to extract some scrabble scores from a legacy system.

The old system stored a list of letters per score:

  • 1 point: "A", "E", "I", "O", "U", "L", "N", "R", "S", "T",
  • 2 points: "D", "G",
  • 3 points: "B", "C", "M", "P",
  • 4 points: "F", "H", "V", "W", "Y",
  • 5 points: "K",
  • 8 points: "J", "X",
  • 10 points: "Q", "Z",

The shiny new scrabble system instead stores the score per letter, which makes it much faster and easier to calculate the score for a word. It also stores the letters in lower-case regardless of the case of the input letters:

  • "a" is worth 1 point.
  • "b" is worth 3 points.
  • "c" is worth 3 points.
  • "d" is worth 2 points.
  • Etc.

Your mission, should you choose to accept it, is to transform the legacy data format to the shiny new format.


A final note about scoring, Scrabble is played around the world in a variety of languages, each with its own unique scoring table. For example, an "E" is scored at 2 in the Māori-language version of the game while being scored at 4 in the Hawaiian-language version.

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 etl_test.rb

To include color from the command line:

ruby -r minitest/pride etl_test.rb


The Jumpstart Lab team http://jumpstartlab.com

Submitting Incomplete Solutions

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


require 'minitest/autorun'
require_relative 'etl'

# Common test data version: 1.0.0 ca9ed58
class EtlTest < Minitest::Test
  def test_a_single_letter
    # skip
    old = {
      1 => ["A"]
    expected = {
      'a' => 1
    assert_equal expected, ETL.transform(old)

  def test_single_score_with_multiple_letters
    old = {
      1 => ["A", "E", "I", "O", "U"]
    expected = {
      'a' => 1,
      'e' => 1,
      'i' => 1,
      'o' => 1,
      'u' => 1
    assert_equal expected, ETL.transform(old)

  def test_multiple_scores_with_multiple_letters
    old = {
      1 => ["A", "E"],
      2 => ["D", "G"]
    expected = {
      'a' => 1,
      'd' => 2,
      'e' => 1,
      'g' => 2
    assert_equal expected, ETL.transform(old)

  def test_multiple_scores_with_differing_numbers_of_letters
    old = {
      1 => ["A", "E", "I", "O", "U", "L", "N", "R", "S", "T"],
      2 => ["D", "G"],
      3 => ["B", "C", "M", "P"],
      4 => ["F", "H", "V", "W", "Y"],
      5 => ["K"],
      8 => ["J", "X"],
      10 => ["Q", "Z"]
    expected = {
      'a' => 1,
      'b' => 3,
      'c' => 3,
      'd' => 2,
      'e' => 1,
      'f' => 4,
      'g' => 2,
      'h' => 4,
      'i' => 1,
      'j' => 8,
      'k' => 5,
      'l' => 1,
      'm' => 3,
      'n' => 1,
      'o' => 1,
      'p' => 3,
      'q' => 10,
      'r' => 1,
      's' => 1,
      't' => 1,
      'u' => 1,
      'v' => 4,
      'w' => 4,
      'x' => 8,
      'y' => 4,
      'z' => 10
    assert_equal expected, ETL.transform(old)
Write your code for the 'ETL' exercise in this file. Make the tests in
`etl_test.rb` pass.

To get started with TDD, see the `README.md` file in your
`ruby/etl` directory.

module ETL
  def transform(chars_by_score)
    score_by_char = {}
    chars_by_score.each { |score, chars| chars.each { |c| score_by_char[c.downcase] = score } }

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