# MicrexIT's solution

## to ETL in the Elm Track

Published at Dec 06 2019 · 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.

## Elm Installation

Refer to the Installing Elm page for information about installing elm.

## Writing the Code

The code you have to write is located inside the `src/` directory of the exercise. Elm automatically installs packages dependencies the first time you run the tests so we can start by running the tests from the exercise directory with:

``````\$ elm-test
``````

To automatically run tests again when you save changes:

``````\$ elm-test --watch
``````

As you work your way through the tests suite in the file `tests/Tests.elm`, be sure to remove the `skip <|` calls from each test until you get them all passing!

## Source

The Jumpstart Lab team http://jumpstartlab.com

## Submitting Incomplete Solutions

It is possible to submit an incomplete solution so you can see how others have completed the exercise.

### Tests.elm

``````module Tests exposing (tests)

import Dict
import Etl
import Expect
import Test exposing (..)

tests : Test
tests =
describe "Etl.transform"
[ test "a single letter" <|
\() ->
Expect.equal
(Dict.fromList [ ( "a", 1 ) ])
(Etl.transform <|
Dict.fromList [ ( 1, [ "A" ] ) ]
)
, skip <|
test "single score with multiple letters" <|
\() ->
Expect.equal
(Dict.fromList
[ ( "a", 1 )
, ( "e", 1 )
, ( "i", 1 )
, ( "o", 1 )
, ( "u", 1 )
]
)
(Etl.transform <|
Dict.fromList
[ ( 1, [ "A", "E", "I", "O", "U" ] )
]
)
, skip <|
test "multiple scores with multiple letters" <|
\() ->
Expect.equal
(Dict.fromList
[ ( "a", 1 )
, ( "d", 2 )
, ( "e", 1 )
, ( "g", 2 )
]
)
(Etl.transform <|
Dict.fromList
[ ( 1, [ "A", "E" ] )
, ( 2, [ "D", "G" ] )
]
)
, skip <|
test "multiple scores with differing numbers of letters" <|
\() ->
Expect.equal
(Dict.fromList
[ ( "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 )
]
)
(Etl.transform <|
Dict.fromList
[ ( 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" ] )
]
)
]``````
``````module Etl exposing (transform)

import Dict exposing (Dict)

transform : Dict Int (List String) -> Dict String Int
transform input =
Dict.toList input
|> List.foldl (\x a -> flattenTuple x :: a) []
|> List.concat
|> Dict.fromList

--   |> Dict.fromList
-- 1. for each tuple in input
-- 2. create a new tuple combing value and char
-- 3. flatten the result
-- 4. add result to list
-- 5. create dictionary

flattenTuple : ( Int, List String ) -> List ( String, Int )
flattenTuple tuple =
Tuple.second tuple
|> List.map (\x -> ( String.toLower x, Tuple.first tuple ))``````