Book Image

Julia 1.0 Programming. - Second Edition

By : Ivo Balbaert
Book Image

Julia 1.0 Programming. - Second Edition

By: Ivo Balbaert

Overview of this book

The release of Julia 1.0 is now ready to change the technical world by combining the high productivity and ease of use of Python and R with the lightning-fast speed of C++. Julia 1.0 programming gives you a head start in tackling your numerical and data problems. You will begin by learning how to set up a running Julia platform, before exploring its various built-in types. With the help of practical examples, this book walks you through two important collection types: arrays and matrices. In addition to this, you will be taken through how type conversions and promotions work. In the course of the book, you will be introduced to the homo-iconicity and metaprogramming concepts in Julia. You will understand how Julia provides different ways to interact with an operating system, as well as other languages, and then you'll discover what macros are. Once you have grasped the basics, you’ll study what makes Julia suitable for numerical and scientific computing, and learn about the features provided by Julia. By the end of this book, you will also have learned how to run external programs. This book covers all you need to know about Julia in order to leverage its high speed and efficiency for your applications.
Table of Contents (17 chapters)
Title Page
Copyright and Credits
Packt Upsell
Contributors
Preface
Index

Dictionaries


When you want to store and look up values based on a unique key, then the dictionary type Dict (also called hash, associative collection, or map in other languages) is what you need. It is basically a collection of two-element tuples of the form (key, value). To define a dictionary d1 as a literal value, the following syntax is used:

// code in Chapter 5\dicts.jl:
d1 = Dict(1 => 4.2, 2 => 5.3)

It returns Dict{Int64,Float64} with two entries: 2 => 5.3 and 1 => 4.2, so there are two key-value tuples here, (1, 4.2) and (2, 5.3); the key appears before the => symbol and the value appears after it, and the tuples are separated by commas.

To explicitly specify the types, use:

d1 = Dict{Int64,Float64}(1 => 4.2, 2 => 5.3)

Note

If you use the former [] notation to try to define a dictionary, you now get Array{Pairs{}} instead:d1 = [1 => 4.2, 2 => 5.3]# 2-element Array{Pair{Int64,Float64},1}:# 1 => 4.2# 2 => 5.3

Here are some other examples:

d2 = Dict{Any,Any...