Custom Enum With Reduce

Mix.install([
  {:kino, github: "livebook-dev/kino", override: true},
  {:kino_lab, "~> 0.1.0-dev", github: "jonatanklosko/kino_lab"},
  {:vega_lite, "~> 0.1.4"},
  {:kino_vega_lite, "~> 0.1.1"},
  {:benchee, "~> 0.1"},
  {:ecto, "~> 3.7"},
  {:math, "~> 0.7.0"},
  {:faker, "~> 0.17.0"},
  {:utils, path: "#{__DIR__}/../utils"},
  {:tested_cell, git: "https://github.com/BrooklinJazz/tested_cell"}
])

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Custom Enum With Reduce

Reduce is an incredibly powerful tool you can leverage in a wide variety of circumstances.

If you’d like to learn more about reduce, there’s an excellent video by Paul Fioravanti.

Kino.YouTube.new("https://www.youtube.com/watch?v=OQrfedclHfk")

We’re going to use Reduce to re-implement several of the Enum module’s functions to show how it can be leveraged for many problems.

Implement the following Enum functions in this CustomEnum function. Each should use Enum.reduce/3 to accomplish the same functionality as the Enum module does.

• map/2
• each/2
• filter/2
• sum/1

ExUnit.start(auto_run: false)

defmodule Assertion do
  use ExUnit.Case

  test "" do
    defmodule CustomEnum do
      def map(collection, function) do
      end

      def each(collection, function) do
      end

      def filter(collection, function) do
      end

      def sum(collection) do
      end
    end

    list = Enum.to_list(1..10)

    assert CustomEnum.map(list, & &1), "Implement the `map/2` function."
    assert is_list(CustomEnum.map(list, & &1)), "`map/2` should return a list."

    assert CustomEnum.map([1, 2, 3], &(&1 * 2)) == [2, 4, 6]

    assert CustomEnum.each(list, & &1), "Implement the `each/2` function."
    assert CustomEnum.each(list, & &1) == :ok, "`each/2` should return :ok."

    assert CustomEnum.filter(list, & &1), "Implement the `filter/2` function."
    assert is_list(CustomEnum.filter(list, & &1)), "`each/2` should return a list."

    assert CustomEnum.filter(list, &amp;(&amp;1 < 5)) == Enum.filter(list, &amp;(&amp;1 < 5))

    assert CustomEnum.sum(list), "Implement the `sum/1` function."
    assert is_integer(CustomEnum.sum(list)), "`sum/1` should return an integer."

    assert CustomEnum.sum(list) == Enum.sum(list)
  end
end

ExUnit.run()

# Make variables and modules defined in the test available.
# Also allows for exploration using the output of the cell.
defmodule CustomEnum do
  def map(collection, function) do
  end

  def each(collection, function) do
  end

  def filter(collection, function) do
  end

  def sum(collection) do
  end
end

Commit Your Progress

Run the following in your command line from the project folder to track and save your progress in a Git commit.

$ git add .
$ git commit -m "finish custom enum with reduce exercise"