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4d47's solution

to ETL in the Perl 6 Track

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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.

Resources

Remember to check out the Perl 6 documentation and resources pages for information, tips, and examples if you get stuck.

Running the tests

There is a test suite and module included with the exercise. The test suite (a file with the extension .t) will attempt to run routines from the module (a file with the extension .pm6). Add/modify routines in the module so that the tests will pass! You can view the test data by executing the command perl6 --doc *.t (* being the name of the test suite), and run the test suite for the exercise by executing the command prove6 . in the exercise directory.

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.t

#!/usr/bin/env perl6
use v6;
use Test;
use JSON::Fast;
use lib $?FILE.IO.dirname;
use ETL;
plan 4;

my $c-data = from-json $=pod.pop.contents;
=head2 Notes
=begin para
The test expects your returned C<Hash> to have
L<type constraints|https://docs.perl6.org/type/Hash#Constraint_value_types>.
Defined C<Str>s for the values, and defined C<Int>s for the keys.
=end para
for $c-data<cases>.values -> %case-set {
  is-deeply(
    transform(Hash[Array[Str:D], Int:D].new(
      .<input>.pairs».&{
        .key.Int => Array[Str:D](.value.Slip)
      }
    )),
    Hash[Int:D, Str:D].new(.<expected>.pairs),
    .<description>
  ) for %case-set<cases>.values;
}

=head2 Canonical Data
=begin code
{
  "exercise": "etl",
  "version": "1.0.0",
  "cases": [
    {
      "comments": [
        "Note:  The expected input data for these tests should have",
        "integer keys (not stringified numbers as shown in the JSON below",
        "Unless the language prohibits that, please implement these tests",
        "such that keys are integers. e.g. in JavaScript, it might look ",
        "like `transform( { 1: ['A'] } );`"
      ],
      "description": "transforms the a set of scrabble data previously indexed by the tile score to a set of data indexed by the tile letter",
      "cases": [
        {
          "description": "a single letter",
          "property": "transform",
          "input": {
            "1": ["A"]
          },
          "expected": {
            "a": 1
          }
        },
        {
          "description": "single score with multiple letters",
          "property": "transform",
          "input": {
            "1": ["A", "E", "I", "O", "U"]
          },
          "expected": {
            "a": 1,
            "e": 1,
            "i": 1,
            "o": 1,
            "u": 1
          }
        },
        {
          "description": "multiple scores with multiple letters",
          "property": "transform",
          "input": {
            "1": ["A", "E"],
            "2": ["D", "G"]
          },
          "expected": {
            "a": 1,
            "d": 2,
            "e": 1,
            "g": 2
          }
        },
        {
          "description": "multiple scores with differing numbers of letters",
          "property": "transform",
          "input": {
             "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"]
          },
          "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
          }
        }
      ]
    }
  ]
}
=end code
unit module ETL:ver<1>;

no precompilation;
no warnings;
no errors;
no bullshit;

sub transform (%input) is export {
    %input ⊶ { %.lc %2 } ⊗ % 
}

What can you learn from this solution?

A huge amount can be learnt 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 I could read more about to develop my understanding?