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Elixir Cookbook
Elixir Cookbook

Elixir Cookbook: Unleash the full power of programming in Elixir with over 60 incredibly effective recipes

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Elixir Cookbook

Chapter 2. Data Types and Structures

This chapter will cover the following recipes:

  • Understanding immutability
  • Adding and subtracting lists
  • Combining tuples into a list
  • Creating and manipulating keyword lists
  • Using pattern matching
  • Pattern matching an HTTPoison response
  • Creating a key/value store with a map
  • Mapping and reducing enumerables
  • Generating lazy (even infinite) sequences
  • Streaming a file as a resource

Understanding immutability

In Elixir, data, once created, is immutable. Whenever some input is passed into a function to be transformed, the original value remains unchanged and a new value is created.

This allows for safe concurrent access to the same data by n processes. It makes concurrency easier to manage, as it is guaranteed that no process can change the original data. Any transformation on the original data will result in new data being created.

Getting ready

To get started, we need to follow these steps:

  1. Create a file, which is transformator.ex, defining the Transformator module by adding the following code:
    defmodule Transformator do
      @default_list [1,2,3,4,5,6]
    
      def get_odd_numbers(list \\ @default_list) do
        Enum.filter(list, fn(x)-> rem(x,2) == 1 end)
      end
    
      def get_even_numbers(list \\ @default_list) do
        Enum.filter(list, fn(x)-> rem(x,2) == 0 end)
      end
    end

    Note

    We define @default_list and use it in both functions preceded by \\. This means that, if no argument...

Adding and subtracting lists

Lists are widely used in functional programming languages, and Elixir is no exception.

Although lists might resemble other languages' arrays, they actually behave more like single-linked lists. Operations with lists are quite common, so in this recipe, we will show you how to add two lists or subtract one list from another.

Getting ready

We will use IEx for this recipe, so start a new session by typing iex in your console.

How to do it…

To add lists, we will use the ++ operator. The steps are as follows:

  1. Create a list named list_one:
    iex(1)> list_one = [1, 3, 5]
    [1, 3, 5]
    
  2. Create a list named list_two:
    iex(2)> list_two = [2, 4, 6, 5]
    [2, 4, 6, 5]
    
  3. Add list_one to list_two:
    iex(3)> list_one ++ list_two
    [1, 3, 5, 2, 4, 6, 5]
    
  4. Add list_two to list_one:
    iex(4)> list_two ++ list_one
    [2, 4, 6, 5, 1, 3, 5]
    

To subtract lists, we will be using the -- operator:

  1. Create a list named list_three:
    iex(5)> list_three = [1, 2, 3, 4, 5, 7, 8, 9]
    [1, 2, 3, 4, 5, 7...

Combining tuples into a list

Elixir has a tuple data type. A tuple, like a list, can contain different types at the same time but guarantees that its elements are stored contiguously in memory.

Tuples are declared using brackets ({}) and are often used as function return values and in-function pattern matching.

Getting ready

In this recipe, we will be using an IEx session. Start it by executing iex in your console.

How to do it…

We will create two tuples, one with atoms and one with integers, and then we will combine them. To do so, we need to convert them into lists:

  1. Create tuple_one:
    iex(1)> tuple_one = {:one, :two, :three}
    {:one, :two, :three}
    
  2. Create tuple_two:
    iex(2)> tuple_two = {1, 2, 3, 4}
    {1, 2, 3, 4}
    
  3. Try to interpolate these two tuples by combining each value on the nth position of tuple_one with the nth value of tuple_two. We will be using the Enum.zip/2 function:
    iex(3)> Enum.zip(tuple_one,tuple_two)
    ** (Protocol.UndefinedError) protocol Enumerable not implemented for...

Creating and manipulating keyword lists

Tuples are often used to represent associative data structures. In Elixir, a list of two element tuples whose first element is an atom is called a keyword list.

Keyword lists have some particular features:

  • They maintain the order of the elements as defined when creating and adding elements
  • They allow repeated keys

Getting ready

Start a new IEx session by entering iex in your command line.

How to do it…

We will follow these steps to create and manipulate keyword lists:

  1. Create a list with three tuples:
    iex(1)> t1 = {:jane, 23}
    iex(2)> t2 = {:jill, 44}
    iex(3)> t3 = {:joe, 32}
    iex(4)> kw_list = [t1, t2, t3]
    [jane: 23, jill: 44, joe: 32]
    
  2. Add a new entry at the end of the list:
    iex(5)> kw_list = kw_list ++ [anthony: 22]
    [jane: 23, jill: 44, joe: 32, anthony: 22]
    
  3. Add a new entry at the beginning of the list:
    iex(6)> kw_list = [zoe: 28] ++ kw_list
    [zoe: 28, jane: 23, jill: 44, joe: 32, anthony: 22]
    
  4. Add an already existing key to the list:
    iex...

Using pattern matching

In some of the previous recipes, we've been using the = operator. When we execute something like a = 1, we are not performing an assignment; we are, instead, binding the value 1 to a.

This is actually pattern matching in its simplest form. The = operator is, in fact, called the match operator.

Getting ready

Start a new IEx session in your console.

How to do it…

To exercise our pattern matching techniques, we will follow these steps:

  1. Let's create a keyword list with our friends' birthdays:
    iex(1)> birthday_list = [andrew: "October 2nd", jim: "May 1st", carrie: "September 23rd", Carla: "August 30th"]
    [andrew: "October 2nd", jim: "May 1st", carrie: "September 23rd",carla: "August 30th"]
    
  2. Now, we will be getting the first element of the list (also known as head of the list):
    iex(2)> [head|tail] = birthday_list
    [andrew: "October 2nd", jim: "May 1st", carrie...

Pattern matching an HTTPoison response

HTTPoison is an HTTP client for Elixir. We have already used it in the Managing dependencies recipe of Chapter 1, Command Line.

In this recipe, we will create a simple application that will take a URL and fetch the corresponding page, returning either the body or the headers of that request.

Getting ready

We will be using the get_pages application. You will find it in the source code of this book. The steps are as follows:

  1. Enter the application directory:
    > cd get_pages
    
  2. Fetch the dependencies and compile them:
    > mix deps.get && mix deps.compile
    
  3. Start the application:
    > iex –S mix
    

How to do it…

To get an HTTP response and perform pattern matching on it, we will follow these steps:

  1. Issue a request to fetch the elixir-lang main page and take the headers from the response:
    iex(1)> GetPages.get(:headers, "http://elixir-lang.com")
    

    The result is shown in the following screenshot:

    How to do it…
  2. Now, we will request the main Google page and...

Understanding immutability


In Elixir, data, once created, is immutable. Whenever some input is passed into a function to be transformed, the original value remains unchanged and a new value is created.

This allows for safe concurrent access to the same data by n processes. It makes concurrency easier to manage, as it is guaranteed that no process can change the original data. Any transformation on the original data will result in new data being created.

Getting ready

To get started, we need to follow these steps:

  1. Create a file, which is transformator.ex, defining the Transformator module by adding the following code:

    defmodule Transformator do
      @default_list [1,2,3,4,5,6]
    
      def get_odd_numbers(list \\ @default_list) do
        Enum.filter(list, fn(x)-> rem(x,2) == 1 end)
      end
    
      def get_even_numbers(list \\ @default_list) do
        Enum.filter(list, fn(x)-> rem(x,2) == 0 end)
      end
    end

    Note

    We define @default_list and use it in both functions preceded by \\. This means that, if no argument is...

Adding and subtracting lists


Lists are widely used in functional programming languages, and Elixir is no exception.

Although lists might resemble other languages' arrays, they actually behave more like single-linked lists. Operations with lists are quite common, so in this recipe, we will show you how to add two lists or subtract one list from another.

Getting ready

We will use IEx for this recipe, so start a new session by typing iex in your console.

How to do it…

To add lists, we will use the ++ operator. The steps are as follows:

  1. Create a list named list_one:

    iex(1)> list_one = [1, 3, 5]
    [1, 3, 5]
    
  2. Create a list named list_two:

    iex(2)> list_two = [2, 4, 6, 5]
    [2, 4, 6, 5]
    
  3. Add list_one to list_two:

    iex(3)> list_one ++ list_two
    [1, 3, 5, 2, 4, 6, 5]
    
  4. Add list_two to list_one:

    iex(4)> list_two ++ list_one
    [2, 4, 6, 5, 1, 3, 5]
    

To subtract lists, we will be using the -- operator:

  1. Create a list named list_three:

    iex(5)> list_three = [1, 2, 3, 4, 5, 7, 8, 9]
    [1, 2, 3, 4, 5, 7, 8, 9]
    
  2. Create...

Combining tuples into a list


Elixir has a tuple data type. A tuple, like a list, can contain different types at the same time but guarantees that its elements are stored contiguously in memory.

Tuples are declared using brackets ({}) and are often used as function return values and in-function pattern matching.

Getting ready

In this recipe, we will be using an IEx session. Start it by executing iex in your console.

How to do it…

We will create two tuples, one with atoms and one with integers, and then we will combine them. To do so, we need to convert them into lists:

  1. Create tuple_one:

    iex(1)> tuple_one = {:one, :two, :three}
    {:one, :two, :three}
    
  2. Create tuple_two:

    iex(2)> tuple_two = {1, 2, 3, 4}
    {1, 2, 3, 4}
    
  3. Try to interpolate these two tuples by combining each value on the nth position of tuple_one with the nth value of tuple_two. We will be using the Enum.zip/2 function:

    iex(3)> Enum.zip(tuple_one,tuple_two)
    ** (Protocol.UndefinedError) protocol Enumerable not implemented for {:one...

Creating and manipulating keyword lists


Tuples are often used to represent associative data structures. In Elixir, a list of two element tuples whose first element is an atom is called a keyword list.

Keyword lists have some particular features:

  • They maintain the order of the elements as defined when creating and adding elements

  • They allow repeated keys

Getting ready

Start a new IEx session by entering iex in your command line.

How to do it…

We will follow these steps to create and manipulate keyword lists:

  1. Create a list with three tuples:

    iex(1)> t1 = {:jane, 23}
    iex(2)> t2 = {:jill, 44}
    iex(3)> t3 = {:joe, 32}
    iex(4)> kw_list = [t1, t2, t3]
    [jane: 23, jill: 44, joe: 32]
    
  2. Add a new entry at the end of the list:

    iex(5)> kw_list = kw_list ++ [anthony: 22]
    [jane: 23, jill: 44, joe: 32, anthony: 22]
    
  3. Add a new entry at the beginning of the list:

    iex(6)> kw_list = [zoe: 28] ++ kw_list
    [zoe: 28, jane: 23, jill: 44, joe: 32, anthony: 22]
    
  4. Add an already existing key to the list:

    iex(7...
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Description

This book is intended for users with some knowledge of the Elixir language syntax and basic data types/structures. Although this is a cookbook and no sequential reading is required, the book’s structure will allow less advanced users who follow it to be gradually exposed to some of Elixir’s features and concepts specific to functional programming. To get the most out of this book, you need to be well versed with Erlang.
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Publication date : Feb 19, 2015
Length: 236 pages
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Language : English
ISBN-13 : 9781784397517
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Estimated delivery fee Deliver to Lithuania

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Length: 236 pages
Edition : 1st
Language : English
ISBN-13 : 9781784397517
Category :
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Table of Contents

10 Chapters
1. Command Line Chevron down icon Chevron up icon
2. Data Types and Structures Chevron down icon Chevron up icon
3. Strings and Binaries Chevron down icon Chevron up icon
4. Modules and Functions Chevron down icon Chevron up icon
5. Processes and Nodes Chevron down icon Chevron up icon
6. OTP – Open Telecom Platform Chevron down icon Chevron up icon
7. Cowboy and Phoenix Chevron down icon Chevron up icon
8. Interactions Chevron down icon Chevron up icon
A. Installation and Further Reading Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

Customer reviews

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noname May 13, 2018
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Highly recommended for Elixir developers. I enjoyed reading it. I used it after learning Elixir and trying to apply the knowledge in real life projects.
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Jordan Jul 05, 2015
Full star icon Full star icon Full star icon Full star icon Empty star icon 4
I feel that this book has been misunderstood and is getting somewhat lower ratings than it deserves. The problem is that the title of this book is a bit misleading. Most programming "cookbooks" contain a collection of non-obvious ways to do things, which are commonly needed but not well documented elsewhere.Instead, this book takes the approach of summarizing the standard introductory Elixir topics in the format of "recipes". This actually makes it a great introductory book, or a great way to supplement your reading of the other intro-level Elixir books. I read this book early on my journey to mastering Elixir and I did learn from it a few new concepts and tricks that I didn't get from the other books. It generally helped cement my knowledge of the foundations. Moreover, the author is active in the Elixir community and it is obvious that he has very solid knowledge and valuable insights into the Elixir way of doing things.
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