Avatar of lujanfernaud

lujanfernaud's solution

to ETL in the Ruby Track

Published at Jul 13 2018 · 1 comment
Instructions
Test suite
Solution

Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

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

ETL

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.

Notes

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 exercism help 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

Source

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.

etl_test.rb

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)
  end

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

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

  def test_multiple_scores_with_differing_numbers_of_letters
    skip
    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)
  end

  # Problems in exercism evolve over time, as we find better ways to ask
  # questions.
  # The version number refers to the version of the problem you solved,
  # not your solution.
  #
  # Define a constant named VERSION inside of the top level BookKeeping
  # module, which may be placed near the end of your file.
  #
  # In your file, it will look like this:
  #
  # module BookKeeping
  #   VERSION = 1 # Where the version number matches the one in the test.
  # end
  #
  # If you are curious, read more about constants on RubyDoc:
  # http://ruby-doc.org/docs/ruby-doc-bundle/UsersGuide/rg/constants.html

  def test_bookkeeping
    skip
    assert_equal 1, BookKeeping::VERSION
  end
end
class ETL
  def self.transform(letters)
    letters.each_with_object({}) do |(key, value), hash|
      value.each do |item|
        hash[item.downcase] = key
      end
    end
  end
end

module BookKeeping
  VERSION = 1
end

Community comments

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

I was having trouble making each_with_object work with key, value and hash, and turns out we can do it passing the arguments together, and then the memo object.

each_with_object(obj) { |(*args), memo_obj| ... } → obj

https://ruby-doc.org/core-2.5.0/Enumerable.html#method-i-each_with_object

I saw this in the solution by @bule http://exercism.io/submissions/4302fe7e0a0341b79f2689f6007d6b68

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?