Avatar of w1zeman1p

w1zeman1p's solution

to ETL in the Ruby Track

Published at Jul 13 2018 · 2 comments
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(old)
    old.to_a.inject({}) do |result, (point, letters)|
      letters
        .map(&:downcase)
        .each { |letter| result[letter] = point }
      result
    end
  end
end

Community comments

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Avatar of veronicacannon

What is this structure? letters .map... .each

Avatar of w1zeman1p

@veronicacannon letters is an array of the letters for a specific point. I map those to .downcase so the result is something like 1 => ['a', 'b', 'c'], then for each of those letters, set the value of the resulting hash at the index (letter) to be the point value.

the {} passed to inject is the initial value for result that is considered our accumulator, now for each of the old key value pairs (point and array of letters) we map the letter array to be only lower case letters, then update our accumulator with letter => point value.

What can you learn from this solution?

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