Avatar of JaeHyoLee

JaeHyoLee's solution

to ETL in the Lua Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

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.

Running the tests

To run the tests, run the command busted from within the exercise directory.

Further information

For more detailed information about the Lua track, including how to get help if you're having trouble, please visit the exercism.io Lua language page.

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_spec.lua

local etl = require('etl')

describe('etl', function()
  it('should correctly transform a dataset with a single mapping', function()
    local old = { [1] = { 'A' } }
    local expected = { a = 1 }
    assert.same(expected, etl.transform(old))
  end)

  it('should correctly transform a dataset with multiple mappings', function()
    local old = { [1] = { 'A' }, [2] = { 'D' } }
    local expected = { a = 1, d = 2 }
    assert.same(expected, etl.transform(old))
  end)

  it('should correctly transform a dataset with multiple letters for a score', function()
    local old = { [1] = { 'A', 'E' }, [2] = { 'D', 'G' } }
    local expected = { a = 1, e = 1, d = 2, g = 2 }
    assert.same(expected, etl.transform(old))
  end)

  it('should correctly transform a full dataset', function()
    local 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' }
    }
    local 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.same(expected, etl.transform(old))
  end)
end)
local function transform(old)
  local new = {}
  for key, value in pairs(old) do
    for _, letter in pairs(value) do
      new[letter:lower()] = key
    end    
  end
  return new
end

return { transform = transform }

Community comments

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

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?