# remcopeereboom'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,
#
# 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
#
# http://ruby-doc.org/docs/ruby-doc-bundle/UsersGuide/rg/constants.html

def test_bookkeeping
skip
assert_equal 1, BookKeeping::VERSION
end
end``````
``````module ETL
def self.transform(value_to_letters)
value_to_letters.each_with_object({}) do |(value, letters), letter_to_value|
letters.each { |letter| letter_to_value[letter.downcase] = value }
end
end
end``````

I like naming mappings in the form of a-to-b, if there is a high chance of confusion.

In my Scrabble script I would prefer just having my variable named values like in the previous iteration.

I've been doing the same thing with maps in the past few months. Sometimes I use by instead of to, depending on context (submissions_by_uuid).

### 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?