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  3. Web Scraping in R
  • 1

    Introduction to HTML and Web Scraping

    Free

    In this chapter, you'll be introduced to Hyper Text Markup Language (HTML), a declarative language used to structure modern websites. Using the rvest library, you'll learn how to query simple HTML elements and scrape your first table.

  • 2

    Navigation and Selection with CSS

    Cascading Style Sheets (CSS) describe how HTML elements are displayed on a web page, including colors, fonts, and general layout. In this chapter, you'll learn why CSS selectors and combinators are a crucial ingredient for web scraping.

  • 3

    Advanced Selection with XPATH

    The CSS selectors you got to know in the last chapter are powerful but have their limitations. For example, if you want to select nodes based on the properties of their descendants. XPath to the rescue! Using this query language, you can navigate and scrape even the most hideous HTML.

  • 4

    Scraping Best Practices

    Now that you know how to extract content from web pages, it's time to look behind the curtains. In this final chapter, you’ll learn why HTTP requests are the foundation of every scraping action and how they can be customized to comply with best practices in web scraping.

Initializing

Exercise

Select direct descendants with the child combinator

By now, you surely know how to select elements by type, class, or ID. However, there are cases where these selectors won't work, for example, if you only want to extract direct descendants of the top ul element. For that, you will use the child combinator (>) introduced in the video.

Here, your goal is to scrape a list (contained in the languages_html document) of all mentioned computer languages, but without the accompanying information in the sub-bullets:

  <ul id = 'languages'>
    <li>SQL</li>
    <ul>    
      <li>Databases</li>
      <li>Query Language</li>
    </ul>
    <li>R</li>
    <ul>
      <li>Collection</li>
      <li>Analysis</li>
      <li>Visualization</li>
    </ul>
    <li>Python</li>
  </ul>

Instructions 1/2

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  • 1

    First, gather all the li elements in the nested list shown above and print their text.

  • 2

    Unlike before, try to extract only direct descendants of the top-level ul element, using the child combinator.