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artemkorsakov's solution

to ETL in the C# Track

Published at Feb 27 2019 · 0 comments
Instructions
Test suite
Solution

Note:

This exercise has changed since this solution 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 the tests

To run the tests, run the command dotnet test from within the exercise directory.

Initially, only the first test will be enabled. This is to encourage you to solve the exercise one step at a time. Once you get the first test passing, remove the Skip property from the next test and work on getting that test passing. Once none of the tests are skipped and they are all passing, you can submit your solution using exercism submit Etl.cs

Further information

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

EtlTest.cs

// This file was auto-generated based on version 1.0.0 of the canonical data.

using System.Collections.Generic;
using Xunit;

public class EtlTest
{
    [Fact]
    public void A_single_letter()
    {
        var input = new Dictionary<int, string[]>
        {
            [1] = new[] { "A" }
        };
        var expected = new Dictionary<string, int>
        {
            ["a"] = 1
        };
        Assert.Equal(expected, Etl.Transform(input));
    }

    [Fact(Skip = "Remove to run test")]
    public void Single_score_with_multiple_letters()
    {
        var input = new Dictionary<int, string[]>
        {
            [1] = new[] { "A", "E", "I", "O", "U" }
        };
        var expected = new Dictionary<string, int>
        {
            ["a"] = 1,
            ["e"] = 1,
            ["i"] = 1,
            ["o"] = 1,
            ["u"] = 1
        };
        Assert.Equal(expected, Etl.Transform(input));
    }

    [Fact(Skip = "Remove to run test")]
    public void Multiple_scores_with_multiple_letters()
    {
        var input = new Dictionary<int, string[]>
        {
            [1] = new[] { "A", "E" },
            [2] = new[] { "D", "G" }
        };
        var expected = new Dictionary<string, int>
        {
            ["a"] = 1,
            ["d"] = 2,
            ["e"] = 1,
            ["g"] = 2
        };
        Assert.Equal(expected, Etl.Transform(input));
    }

    [Fact(Skip = "Remove to run test")]
    public void Multiple_scores_with_differing_numbers_of_letters()
    {
        var input = new Dictionary<int, string[]>
        {
            [1] = new[] { "A", "E", "I", "O", "U", "L", "N", "R", "S", "T" },
            [2] = new[] { "D", "G" },
            [3] = new[] { "B", "C", "M", "P" },
            [4] = new[] { "F", "H", "V", "W", "Y" },
            [5] = new[] { "K" },
            [8] = new[] { "J", "X" },
            [10] = new[] { "Q", "Z" }
        };
        var expected = new Dictionary<string, int>
        {
            ["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.Equal(expected, Etl.Transform(input));
    }
}
using System.Collections.Generic;
using System.Linq;

public static class Etl
{
    public static Dictionary<string, int> Transform(Dictionary<int, string[]> old)
    {
        return old.Keys.SelectMany(k => old[k].ToDictionary(v => v.ToLower(), v => k))
            .ToDictionary(pair => pair.Key, pair => pair.Value);
    }
}

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