Book Image

Clojure Programming Cookbook

Book Image

Clojure Programming Cookbook

Overview of this book

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!
Table of Contents (16 chapters)
Clojure Programming Cookbook
About the Authors
About the Reviewer

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:

 #(= 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:

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

Filtering non-nil values

This filters non-nil values:

 (filter #(not...