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artemkorsakov's solution

to ETL in the Go Track

Published at Feb 21 2019 · 0 comments
Test suite

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 the tests

To run the tests run the command go test from within the exercise directory.

If the test suite contains benchmarks, you can run these with the --bench and --benchmem flags:

go test -v --bench . --benchmem

Keep in mind that each reviewer will run benchmarks on a different machine, with different specs, so the results from these benchmark tests may vary.

Further information

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


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.


package etl

import "testing"

type given map[int][]string
type expectation map[string]int

var transformTests = []struct {
	input  given
	output expectation
		given{1: {"A"}},
		expectation{"a": 1},
		given{1: {"A", "E", "I", "O", "U"}},
		expectation{"a": 1, "e": 1, "i": 1, "o": 1, "u": 1},
			1: {"A", "E"},
			2: {"D", "G"},
			"a": 1,
			"e": 1,
			"d": 2,
			"g": 2,
			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, "e": 1, "i": 1, "o": 1, "u": 1, "l": 1, "n": 1, "r": 1, "s": 1, "t": 1,
			"d": 2, "g": 2,
			"b": 3, "c": 3, "m": 3, "p": 3,
			"f": 4, "h": 4, "v": 4, "w": 4, "y": 4,
			"k": 5,
			"j": 8, "x": 8,
			"q": 10, "z": 10,

func equal(actual map[string]int, expectation map[string]int) bool {
	if len(actual) != len(expectation) {
		return false

	for k, actualVal := range actual {
		expectationVal, present := expectation[k]

		if !present || actualVal != expectationVal {
			return false

	return true

func TestTransform(t *testing.T) {
	for _, tt := range transformTests {
		actual := Transform(map[int][]string(tt.input))
		if !equal(actual, tt.output) {
			t.Fatalf("Transform(%v). Expected [%v], Actual [%v]", tt.input, tt.output, actual)

func BenchmarkTransform(b *testing.B) {
	for i := 0; i < b.N; i++ {

		for _, tt := range transformTests {

package etl

import (

// Transform transforms the legacy data format to the shiny new format
func Transform(given map[int][]string) map[string]int {
	result := make(map[string]int)
	for k, v := range given {
		for _, let := range v {
			result[strings.ToLower(let)] = k
	return result

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