🎉 Exercism Research is now launched. Help Exercism, help science and have some fun at research.exercism.io 🎉
Avatar of di98jgu

di98jgu's solution

to ETL in the Erlang Track

Published at Mar 12 2020 · 0 comments
Test suite


This exercise has changed since this solution was written.

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


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.


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

In order to run the tests, issue the following command from the exercise directory:

For running the tests provided, rebar3 is used as it is the official build and dependency management tool for erlang now. Please refer to the tracks installation instructions on how to do that.

In order to run the tests, you can issue the following command from the exercise directory.

$ rebar3 eunit


For detailed information about the Erlang track, please refer to the help page on the Exercism site. This covers the basic information on setting up the development environment expected by the exercises.


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.


%% Based on canonical data version 1.0.0
%% https://github.com/exercism/problem-specifications/raw/master/exercises/etl/canonical-data.json
%% This file is automatically generated from the exercises canonical data.



'1_a_single_letter_test'() ->
        {1, ["A"]}
        {"a", 1}

'2_single_score_with_multiple_letters_test'() ->
        {1, ["A", "E", "I", "O", "U"]}
        {"a", 1},
        {"e", 1},
        {"i", 1},
        {"o", 1},
        {"u", 1}

'3_multiple_scores_with_multiple_letters_test'() ->
        {1, ["A", "E"]},
        {2, ["D", "G"]}
        {"a", 1},
        {"d", 2},
        {"e", 1},
        {"g", 2}

'4_multiple_scores_with_differing_numbers_of_letters_test'() ->
        {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"]}
        {"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}


%% --- Debug -----------------------------------------------
-define(PRINT(Var), io:format("DEBUG: ~p:~p - ~p~n~n ~p~n~n", [?MODULE, ?LINE, ??Var, Var])).
%% ---------------------------------------------------------

read_legacy_row(Model, _Score, []) ->
read_legacy_row(Model, Score, [Letter|Next]) ->
    read_legacy_row(model_add(Model, Letter, Score), Score, Next). 

read_legacy_record(Model, []) ->
read_legacy_record(Model, [Row|Next]) ->
    {Score, Letters} = Row,
    read_legacy_record(read_legacy_row(Model, Score, Letters), Next).

read_legacy(Model, Source) ->
    read_legacy_record(Model, Source).

write_record_next(done, Destination) ->
write_record_next(Model, []) ->
    {Letter, Score} = model_get(Model),
    write_record_next(model_next(Model), [{Letter, Score}]);
write_record_next(Model, Destination) ->
    {Letter, Score} = model_get(Model),
    write_record_next(model_next(Model), [{Letter, Score}|Destination]).

write(Model) ->
    write_record_next(model_first(Model), []).

model_new() ->
    {{}, {[], []}}.

model_key_normalize(Key) ->

model_add({{}, {Left, Right}}, Key, Value) ->
    {{model_key_normalize(Key), Value}, {Left, Right}};
model_add({Row, {Left, Right}}, Key, Value) ->
    {{model_key_normalize(Key), Value}, {[Row|Left], Right}}. 
model_get({Row, _Rows}) ->

model_first({Row, {[], []}}) ->
    {Row, {[], []}};
model_first({Row, {Left, Right}}) ->
    [First|Rows] = lists:reverse(Left) ++ [Row|Right],
    {First, {[], Rows}}.

model_next({_Row, {_Left, []}}) ->
model_next({Row, {Left, [Next|Right]}}) ->
    {Next, {[Row|Left], Right}}.

transform(Old) ->
    Model = read_legacy(model_new(), Old),

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?