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Clojure Programming Cookbook
Clojure Programming Cookbook

Clojure Programming Cookbook: Handle every problem you come across in the world of Clojure programming with this expert collection of recipes

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Profile Icon Modrzyk Profile Icon Makoto Hashimoto
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€41.99
Full star icon Full star icon Full star icon Empty star icon Empty star icon 3 (1 Ratings)
Paperback Oct 2016 618 pages 1st Edition
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Arrow left icon
Profile Icon Modrzyk Profile Icon Makoto Hashimoto
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€41.99
Full star icon Full star icon Full star icon Empty star icon Empty star icon 3 (1 Ratings)
Paperback Oct 2016 618 pages 1st Edition
eBook
€22.99 €32.99
Paperback
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Clojure Programming Cookbook

Chapter 2. Interacting with Collections

In this chapter, we will cover the following topics:

  • Clojure collections and their basic functions
  • Accessing and updating elements from collections
  • Filtering elements from collections
  • Transforming and sorting collections
  • Merging and splitting collections
  • How to become lazy

Introduction

Clojure belongs to the Lisp language family, and Lisp can handle collections in a very cool and efficient way. Clojure inherits rich and cool sets from Lisp. In this chapter, we will show basic and advanced recipes for manipulating collections.

Another advantage of manipulating collections in Clojure is to guarantee immutability. In the case of large or concurrent applications, mutability causes unintended behaviors resulting in serious bugs.

After reading this chapter, you'll be able to write Clojure code to handle collections with a lot of fun.

Clojure collections and their basic functions

There are four collection types in Clojure:

  • Lists
  • Vectors
  • Maps
  • Sets

In this recipe, we will describe what these types are and some basic functions for them.

Getting ready

You only need REPL described in the recipe Repl up! in Chapter 1, Live Programming with Clojure, and no additional libraries. Start REPL so that you can review the sample code in this recipe.

How to do it...

We will learn collection types in Clojure including lists, vectors, maps, and sets. We will learn how to create them and use basic functions for them.

Lists

Lists are commonly used in Lisp. Clojure also supports the list data type. Lists are internally implemented as a linked list. To create a list, begin with quote (') and then enclose elements with (). If you want to create an empty list, use ' (), or (list):

'("A Study in Scarlet" 
"The Sign of the Four" 
"The Hound of the Baskervilles" 
"The Valley of Fear") 
;;=> ...

Accessing and updating elements from collections

In this recipe, we will teach you how to access elements and update elements in collections.

Getting ready

You only need REPL, as described in the recipe in Chapter 1, Live Programming with Clojure, and no additional libraries. Start REPL so that you can review the sample code in this recipe.

How to do it...

Let's start with accessing collections.

Accessing collections using the nth function

nth gets the nthelement from collections. The second argument of nth starts from 0 and throws an exception if the second argument is larger than the number of elements minus 1:

(nth [1 2 3 4 5] 1) 
;;=> 2 
(nth '("a" "b" "c" "d" "e") 3) 
;;=> "d" 
(nth [1 2 3] 3) 
;;=> IndexOutOfBoundsException   clojure.lang.PersistentVector.arrayFor (PersistentVector.java:153) 

If you would like to avoid such an exception, use the third argument as the return value:

(nth [1 2 3] 3 nil) 
;;...

Filtering elements from collections

This section quickly shows how to select only some elements of a Clojure sequence.

Getting ready

The first parts of the recipe do not need any special preparation, but the final section needs the core.async library to be added to your project.clj file (or any other dependency management you are using):

:dependencies [ 
     [org.clojure/clojure "1.8.0"] 
    [org.clojure/core.async "0.2.371"]] 

How to do it...

There are four main functions to filter elements:

  • filter
  • keep and keep-indexed
  • remove
  • take and take-while

Let's go through a few simple examples.

Filtering multiples of three

The following code filters numbers that are multiples of three:

(filter  
 #(= 0 (rem % 3)) 
 (range 1 10)) 
 ; (3 6 9) 

Filtering items of a map

This filters keys that are in the map, which is used as a function here:

(filter  
 {:b 2 :c 3}  
 [:a :b]) 
; (:b) 

Filtering non-nil values

This filters non-nil values:

 (filter #(not (nil? %)) 
         &apos...

Transforming and sorting collections

In this section, we will review different ways of getting sorted. All you ever wanted to know about sorting Clojure collections will be in this recipe.

As usual, Clojure offers practical ways of using the same functions in generic situations so as to refine your sorting to the particular needs.

In almost all cases, the sorted collection is a new instance of the input, but we will also look at corner cases when using Clojure/Java interop, where the collection may keep an internal state to be aware of.

Getting ready

This section does not make use of any external libraries, so you can just start REPL and be ready.

How to do it...

To get a good grasp of how to use the different sorting methods, we will go through the most important functions first, and we will look at the under-the-hood functions in the next sub-section.

Using built-in sort

The built-in sort is easy to grasp and use. As with the usual Clojure functions, a new collection is created on applying sorting...

Merging and splitting collections

Sometimes, you'd like to merge multiple collections into a single collection or split a single collection into multiple collections. Let's have a look these cases.

Getting ready

You only need REPL, described in the Repl up! recipe in Chapter 1, Live Programming with Clojure, and no additional libraries. Start REPL, and you can review the sample code in this recipe.

How to do it...

Let's see how to merge and split collections.

Using merge and merge-with for merging

The merge function merges multiple maps into a single map. If there are the same keys among maps in arguments, latter entries override former entries:

(merge {:a 1 :b 2 :c 3} {:c 4 :d 5 :e 6}) 
;;=> {:a 1, :b 2, :c 4, :d 5, :e 6} 
(merge {:a 1 :b 2 :c 3} {:c 4 :d 5 :e 6} {:c 7 :f 4 :g 6}) 
;;=> {:a 1, :b 2, :c 7, :d 5, :e 6, :f 4, :g 6} 

The merge-with function is more amazing:

(def nicos-fruits 
  {:apple 10 :melon 15 :orange 2 :pear 12} 
  ) 
;;=> #'collection.core...

Introduction


Clojure belongs to the Lisp language family, and Lisp can handle collections in a very cool and efficient way. Clojure inherits rich and cool sets from Lisp. In this chapter, we will show basic and advanced recipes for manipulating collections.

Another advantage of manipulating collections in Clojure is to guarantee immutability. In the case of large or concurrent applications, mutability causes unintended behaviors resulting in serious bugs.

After reading this chapter, you'll be able to write Clojure code to handle collections with a lot of fun.

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Key benefits

  • Discover a wide variety of practical cases and real world techniques to enhance your productivity with Clojure.
  • Learn to resolve the everyday issues you face with a functional mindset using Clojure
  • You will learn to write highly efficient, more productive, and error-free programs without the risk of deadlocks and race-conditions

Description

When it comes to learning and using a new language you need an effective guide to be by your side when things get rough. For Clojure developers, these recipes have everything you need to take on everything this language offers. This book is divided into three high impact sections. The first section gives you an introduction to live programming and best practices. We show you how to interact with your connections by manipulating, transforming, and merging collections. You’ll learn how to work with macros, protocols, multi-methods, and transducers. We’ll also teach you how to work with languages such as Java, and Scala. The next section deals with intermediate-level content and enhances your Clojure skills, here we’ll teach you concurrency programming with Clojure for high performance. We will provide you with advanced best practices, tips on Clojure programming, and show you how to work with Clojure while developing applications. In the final section you will learn how to test, deploy and analyze websocket behavior when your app is deployed in the cloud. Finally, we will take you through DevOps. Developing with Clojure has never been easier with these recipes by your side!

Who is this book for?

This book is for Clojure developers who have some Clojure programming experience and are well aware of their shortcomings. If you want to learn to tackle common problems, become an expert, and develop a solid skill set, then this book is for you.

What you will learn

  • Manipulate, access, filter, and transform your data with Clojure
  • Write efficient parallelized code through Clojure abstractions
  • Tackle Complex Concurrency easily with Reactive Programming
  • Build on Haskell abstractions to write dynamic functional tests
  • Write AWS Lambda functions effortlessly
  • Put Clojure in use into your IoT devices
  • Use Clojure with Slack for instant monitoring
  • Scaling your Clojure application using Docker
  • Develop real-time system interactions using MQTT and websockets
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Table of Contents

10 Chapters
1. Live Programming with Clojure Chevron down icon Chevron up icon
2. Interacting with Collections Chevron down icon Chevron up icon
3. Clojure Next Chevron down icon Chevron up icon
4. File Access and the Network Chevron down icon Chevron up icon
5. Working with Other Languages Chevron down icon Chevron up icon
6. Concurrency and Parallelism Chevron down icon Chevron up icon
7. Advanced Tips Chevron down icon Chevron up icon
8. Web Applications Chevron down icon Chevron up icon
9. Testing Chevron down icon Chevron up icon
10. Deployment and DevOps Chevron down icon Chevron up icon

Customer reviews

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Full star icon Full star icon Full star icon Empty star icon Empty star icon 3
(1 Ratings)
5 star 0%
4 star 0%
3 star 100%
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1 star 0%
el May 05, 2017
Full star icon Full star icon Full star icon Empty star icon Empty star icon 3
While this book covers a lot of ground, and I think that in terms of breadth of coverage there is no other book like it, the quality of recipes is varied. Examples are not always very clear, and the general impression is of a general shabbiness. Would I buy it again? yes, because of the amount of content.
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