Automated Data Collection with R: A Practical Guide to Web Scraping and Text Mining

Automated Data Collection with R: A Practical Guide to Web Scraping and Text Mining

Simon Munzert, Christian Rubba, Dominic Nyhuis, Peter Meiner

Language: English

Pages: 489

ISBN: 2:00313065

Format: PDF / Kindle (mobi) / ePub


A hands on guide to web scraping and text mining for both beginners and experienced users of R Introduces fundamental concepts of the main architecture of the web and databases and covers HTTP, HTML, XML, JSON, SQL.

Provides basic techniques to query web documents and data sets (XPath and regular expressions). An extensive set of exercises are presented to guide the reader through each technique.

Explores both supervised and unsupervised techniques as well as advanced techniques such as data scraping and text management. Case studies are featured throughout along with examples for each technique presented. R code and solutions to exercises featured in the book are provided on a supporting website.

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after a pause of one second, which is specified with the Sys.sleep() function. There is no official rule how often a polite scraper should access a page. As a rule of thumb we try to make no more than one or two requests per second if Crawl-delay in the robots.txt does not dictate more modest request behavior. Finally, writing a modest scraper is not only a question of efficiency but also of politeness. There is often no reason to scrape pages daily or repeat the same task over and over again.

congress as the free fields and position, state, and party as the fields with given options. We are interested in a list of all the senators in the 111th Senate, hence we specify these two values and leave the other fields open. The URL destination is specified in the form tag. For this request, we use the RCurl package which provides the useful postForm(). Note that the form expects application/x-www-form-urlencoded encoded content, so we add the argument style = ’POST’. Posting a form The

are set to NA. R> temptable <- as.numeric(unlist(temptable)) Having discarded the table structure and kept only the temperatures, we now have to reconstruct the days and months belonging to the temperatures. Fortunately, unlist() always decomposes data frames in the same way. It starts with all rows of the first column and appends the values of the following columns one by one. As we know that in the temperature tables rows referred to days and columns to months, we can simply repeat the day

client–server communication (see Figure 5.5). HTTPS URLs have the scheme https and use the port 443 by default.16 Figure 5.5 The principle of HTTPS HTTPS serves two purposes: First, it helps the client to ensure that the server it talks to is trustworthy (server authentication). Second, it provides encryption of client–server communication so that users can be reasonably sure that nobody else reads what is exchanged during communication. The SSL/TLS security layer runs as a sublayer of the

fortunes2.html. The Elements panel is particularly useful for learning about the links between specific HTML code and its corresponding graphical representation in the page view. By hovering your cursor over a node in the WDT, the respective element in the HTML page view is highlighted. To do the reverse and identify the code piece that produces an element in the page view, click on the magnifying glass symbol at the top right of the panel bar. Now, once you click on an element in the page view,

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