Weighted Voting

Mix.install([
  {:jason, "~> 1.4"},
  {:kino, "~> 0.8.0", override: true},
  {:youtube, github: "brooklinjazz/youtube"},
  {:hidden_cell, github: "brooklinjazz/hidden_cell"}
])

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Weighted Voting

In the previous Counting Votes exercise, we created a module to count a list of votes. For example, users would vote for their favorite animal to decide if :birds, :dogs, or :cats were more popular.

Now, you’re going to create a WeightedVoting.count/2 that can count the number of votes for a single value such as :dogs or :cats. provided in a keyword list.

WeightedVoting.count([cats: 10, dogs: 20, dogs: 20], :dogs)
40

You’re also going to create a WeightedVoting.tally/1 function that will count the votes provided in a keyword list, and return the results as a keyword list like so.

WeightedVoting.tally([cats: 10, dogs: 20, dogs: 20])
[cats: 10, dogs: 40]

Example Solution

defmodule WeightedVoting do
  def count(votes, vote_to_count) do
    Enum.reduce(votes, 0, fn {key, value}, acc ->
      if key == vote_to_count do
        acc + value
      else
        acc
      end
    end)
  end

  def tally(votes) do
    Enum.reduce(votes, [], fn {key, vote_count}, acc ->
      Keyword.update(acc, key, vote_count, fn existing_value ->
        existing_value + vote_count
      end)
    end)
  end

  def tally_map(votes) do
    Enum.reduce(votes, %{}, fn {key, vote_count}, acc ->
      Map.update(acc, key, vote_count, fn existing_value ->
        existing_value + vote_count
      end)
    end)
  end
end

Implement the WeightedVoting module as documented below.

defmodule WeightedVoting do
  @doc """
  Count the total number of votes for some key in a keyword list.

  ## Examples

    iex> WeightedVoting.count([dogs: 20, dogs: 10], :dogs)
    30
    iex> WeightedVoting.count([cats: 10, dogs: 20, dogs: 30], :dogs)
    50
    iex> WeightedVoting.count([cats: 10, dogs: 20, dogs: 10, cats: 30], :cats)
    40
  """
  def count(votes, vote_to_count) do
  end

  @doc """
  Tally the total number of votes in a keyword list, and return
  the results as a keyword list.

  The keyword list should be sorted in alphabetical order.

  ## Examples

    iex> WeightedVoting.tally([dogs: 20, dogs: 10])
    [dogs: 30]
    iex> WeightedVoting.tally([cats: 10, dogs: 20, dogs: 10])
    [cats: 10, dogs: 30]
    iex> WeightedVoting.tally([cats: 10, dogs: 20, cats: 20, dogs: 10, birds: 20])
    [birds: 20, cats: 30, dogs: 30]
  """
  def tally(votes) do
  end
end

Bonus: Tally Map

Create a WeightedVoting.tally_map/1 function which returns a map instead of a keyword list. You may copy the following code into the WeightedVoting module above to get started.

  @doc """
  Tally the total number of votes in a keyword list, and return
  the results as a map.

  ## Examples

    iex> WeightedVoting.tally_map([dogs: 20, dogs: 10])
    %{dogs: 30}
    iex> WeightedVoting.tally_map([cats: 10, dogs: 20, dogs: 10])
    %{cats: 10, dogs: 30}
    iex> WeightedVoting.tally_map([cats: 10, dogs: 20, cats: 20, dogs: 10, birds: 20])
    %{birds: 20, cats: 30, dogs: 30}
  """
  def tally_map(votes) do
  end

Mark As Completed

file_name = Path.basename(Regex.replace(~r/#.+/, __ENV__.file, ""), ".livemd")

save_name =
  case Path.basename(__DIR__) do
    "reading" -> "weighted_voting_reading"
    "exercises" -> "weighted_voting_exercise"
  end

progress_path = __DIR__ <> "/../progress.json"
existing_progress = File.read!(progress_path) |> Jason.decode!()

default = Map.get(existing_progress, save_name, false)

form =
  Kino.Control.form(
    [
      completed: input = Kino.Input.checkbox("Mark As Completed", default: default)
    ],
    report_changes: true
  )

Task.async(fn ->
  for %{data: %{completed: completed}} <- Kino.Control.stream(form) do
    File.write!(
      progress_path,
      Jason.encode!(Map.put(existing_progress, save_name, completed), pretty: true)
    )
  end
end)

form

Commit Your Progress

Run the following in your command line from the curriculum folder to track and save your progress in a Git commit. Ensure that you do not already have undesired or unrelated changes by running git status or by checking the source control tab in Visual Studio Code.

$ git checkout -b weighted-voting-exercise
$ git add .
$ git commit -m "finish weighted voting exercise"
$ git push origin weighted-voting-exercise

Create a pull request from your weighted-voting-exercise branch to your solutions branch. Please do not create a pull request to the DockYard Academy repository as this will spam our PR tracker.

DockYard Academy Students Only:

Notify your teacher by including @BrooklinJazz in your PR description to get feedback. You (or your teacher) may merge your PR into your solutions branch after review.

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