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# shmibs's solution

## to ETL in the Elixir Track

Published at Jul 13 2018 · 0 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.

## Running tests

Execute the tests with:

``````\$ elixir etl_test.exs
``````

### Pending tests

In the test suites, all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by commenting out the relevant `@tag :pending` with a `#` symbol.

For example:

``````# @tag :pending
test "shouting" do
assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end
``````

Or, you can enable all the tests by commenting out the `ExUnit.configure` line in the test suite.

``````# ExUnit.configure exclude: :pending, trace: true
``````

For more detailed information about the Elixir track, please see the help 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_test.exs

``````if !System.get_env("EXERCISM_TEST_EXAMPLES") do
end

ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)

defmodule TransformTest do
use ExUnit.Case

# @tag :pending
test "transform one value" do
old = %{1 => ["WORLD"]}
expected = %{"world" => 1}

assert ETL.transform(old) == expected
end

@tag :pending
test "transform more values" do
old = %{1 => ["WORLD", "GSCHOOLERS"]}
expected = %{"world" => 1, "gschoolers" => 1}

assert ETL.transform(old) == expected
end

@tag :pending
test "more keys" do
old = %{1 => ["APPLE", "ARTICHOKE"], 2 => ["BOAT", "BALLERINA"]}

expected = %{
"apple" => 1,
"artichoke" => 1,
"boat" => 2,
"ballerina" => 2
}

assert ETL.transform(old) == expected
end

@tag :pending
test "full dataset" do
old = %{
1 => ~W(A E I O U L N R S T),
2 => ~W(D G),
3 => ~W(B C M P),
4 => ~W(F H V W Y),
5 => ~W(K),
8 => ~W(J X),
10 => ~W(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 ETL.transform(old) == expected
end
end``````
``````defmodule ETL do
@doc """
Transform an index into an inverted index.

## Examples

iex> ETL.transform(%{"a" => ["ABILITY", "AARDVARK"], "b" => ["BALLAST", "BEAUTY"]})
%{"ability" => "a", "aardvark" => "a", "ballast" => "b", "beauty" =>"b"}
"""
@spec transform(map) :: map
def transform(map) do
Map.keys(map)
|> Enum.reduce(%{}, &(push_inverted &1, &2, map) )
end

defp push_inverted(k, m, om) do
Stream.map(om[k], &String.downcase/1)
|> Enum.reduce(m, &(Map.put &2, &1, k) )
end
end``````