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R Web Scraping Quick Start Guide
R Web Scraping Quick Start Guide

R Web Scraping Quick Start Guide: Techniques and tools to crawl and scrape data from websites

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R Web Scraping Quick Start Guide

XML Path Language and Regular Expression Language

XPath primarily handles the nodes of XML 1.0 or XML 1.1 trees. It is used to represent the hierarchical structure of an XML document. XPath uses non-XML syntax and works on the logical structure of XML documents. This structure is also known as the data model. XPath is designed to be used embedded into a programming language. It has a natural subset that can be used for mapping.

A regular expression, regex or regexp, represents a search model used in computer science. Regex emerged as a result of the work of the American mathematician Stephen Cole Kleene in the 1950s. It is also being used with Unix text-processing programs. There are different forms of syntax for writing regular expressions: the POSIX standard and Perl syntax. A regular expression in search engines is used in search and replace operations and lexical analysis...

XML Path (XPath)

XPath is a syntax that provides functionality between XSL transformations and XPointer. It deals with parts of an XML document. It is used to manipulate strings, numbers, and Boolean expressions to handle the relevant parts of the XML document. XPath defines the path to a listener for each node type in an XML document. The primary syntactical structure in XPath is the expression. An expression is used to obtain an object that has one of the following four basic types:

  • Node-set
  • Boolean
  • Number
  • String

Key words in XPath are not written separately and they are written using lowercase characters. Each node in XML has a unique ID, a typed value, and a string value. Also, some nodes can even have a name. The value written to a node can be zero or atomic value strings. A sequence containing exactly one element is called a singleton. An item is identical to a singular...

Regular expression language (Regex)

Regular expressions are extremely useful when they are used to extract information from any text by searching for a specific sequence of ASCII or Unicode characters. The web is frequently used in search operations. One of the most impressive features of Regex is that it can be used in almost all programming languages. Basically, a regular expression is a formula that helps explain a text. RegEx's name comes from the mathematical theory underlying the idea. It is usually shortened to regex or regexp.

You can use regular expressions with a text bean that you can usually access using your programming language. If it is known how a Regex engine works, it will be easier to generate regexes. It will be easy to understand why you cannot do what you expect with a regular expression and write more complex expressions.

There are basically only two...

Exercises on RegEx and XPath

In this part, we are going to do some exercises that will be about writing XPaths and RegEx rules. For this purpose, we will use some open source tools.

One of the best open source platforms for practising writing RegEx rules is https://regex101.com/:

Regular expressions on regex101.com

As you see from the screenshot of regex101.com, the following is true:

  • You can add some text strings to the Test String part and you can add your regular expressions to the Regular Expression part.
  • On the Test String part, you will be able to see the matched strings.
  • For testing your XPath rules, you can use Google Chrome's developer tools.
  • You can reach this menu through the More Tools section; click on those three dots on your Chrome browser, as shown in the following screenshot:
Developer tools option on the web page
  • When you click Developer tools, you...

Summary

In this chapter, we have tried to focus on the idea behind XPath and RegEx; we became familiar with tools to write/test RegEx and XPath rules. In the exercise section, we focused on a real-life example and tried to write RegEx and XPath rules by using the tools that were mentioned.

In the next chapter, we will talk about the rvest library of R. We will investigate how it works and how to build scraping systems using the rvest library.

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Key benefits

  • Techniques, tools and frameworks for web scraping with R
  • Scrape data effortlessly from a variety of websites
  • Learn how to selectively choose the data to scrape, and build your dataset

Description

Web scraping is a technique to extract data from websites. It simulates the behavior of a website user to turn the website itself into a web service to retrieve or introduce new data. This book gives you all you need to get started with scraping web pages using R programming. You will learn about the rules of RegEx and Xpath, key components for scraping website data. We will show you web scraping techniques, methodologies, and frameworks. With this book's guidance, you will become comfortable with the tools to write and test RegEx and XPath rules. We will focus on examples of dynamic websites for scraping data and how to implement the techniques learned. You will learn how to collect URLs and then create XPath rules for your first web scraping script using rvest library. From the data you collect, you will be able to calculate the statistics and create R plots to visualize them. Finally, you will discover how to use Selenium drivers with R for more sophisticated scraping. You will create AWS instances and use R to connect a PostgreSQL database hosted on AWS. By the end of the book, you will be sufficiently confident to create end-to-end web scraping systems using R.

Who is this book for?

This book is for R programmers who want to get started quickly with web scraping, as well as data analysts who want to learn scraping using R. Basic knowledge of R is all you need to get started with this book.

What you will learn

  • Write and create regEX rules
  • Write XPath rules to query your data
  • Learn how web scraping methods work
  • Use rvest to crawl web pages
  • Store data retrieved from the web
  • Learn the key uses of Rselenium to scrape data

Product Details

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Publication date : Oct 31, 2018
Length: 114 pages
Edition : 1st
Language : English
ISBN-13 : 9781789138733
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Product Details

Publication date : Oct 31, 2018
Length: 114 pages
Edition : 1st
Language : English
ISBN-13 : 9781789138733
Category :
Languages :
Concepts :

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Table of Contents

6 Chapters
Introduction to Web Scraping Chevron down icon Chevron up icon
XML Path Language and Regular Expression Language Chevron down icon Chevron up icon
Web Scraping with rvest Chevron down icon Chevron up icon
Web Scraping with Rselenium Chevron down icon Chevron up icon
Storing Data and Creating Cronjob Chevron down icon Chevron up icon
Other Books You May Enjoy Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Half star icon Empty star icon Empty star icon 2.7
(3 Ratings)
5 star 33.3%
4 star 0%
3 star 0%
2 star 33.3%
1 star 33.3%
rguru Nov 22, 2018
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Awesome book, its full of examples and really good explanation style.
Amazon Verified review Amazon
Jamie Tock Aug 12, 2019
Full star icon Full star icon Empty star icon Empty star icon Empty star icon 2
It is written as if you are already familiar with many of the concepts that are needed to succeed with web scraping. Detail is very sparse and abstract for the parts needed to actually do the web scraping. I got virtually zero use of it. There are other resources that are much better and more useful.
Amazon Verified review Amazon
Warren Sep 30, 2020
Full star icon Empty star icon Empty star icon Empty star icon Empty star icon 1
Really lacking. The tutorials are dated and won't work. The book is written by a doctoral candidate, not a professor. Too short. Never actually covers R and RStudio.
Amazon Verified review Amazon
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