April 2025
Intermediate to advanced
578 pages
13h 35m
Portuguese (Portugal, Brazil)
Content preview from R for Data Science, 2ª Edição
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Capítulo 24. Raspagem da Web
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Introdução
Este capítulo apresenta-te as noções básicas de Web scraping com o rvest. A raspagem da Web é uma ferramenta útil para extrair dados de páginas da Web. Alguns sites oferecem uma API, um conjunto de pedidos HTTP estruturados que retornam dados como JSON, que podes manipular usando as técnicas do Capítulo 23. Sempre que possível, deves utilizar a API,1 porque, normalmente, ela te dará dados mais confiáveis. Infelizmente, porém, a programação com APIs da Web está fora do escopo deste livro. Em vez disso, vamos ensinar scraping, uma técnica que funciona independentemente de um site fornecer ou não uma API.
Neste capítulo, discutiremos primeiro a ética e as legalidades da raspagem antes de mergulharmos nos conceitos básicos de HTML. Em seguida, aprende as noções básicas de seletores CSS para localizar elementos específicos na página e como utilizar funções rvest para obter dados de texto e atributos do HTML para o R. Discutiremos algumas técnicas para descobrir qual o seletor CSS necessário para a página que está a recolher, antes de terminar com alguns estudos de caso e uma breve discussão sobre sites dinâmicos.
Pré-requisitos
Neste capítulo, vamos concentrar-nos nas ferramentas fornecidas pelo rvest. O rvest é um membro do tidyverse mas não é um membro principal, por isso terás de o carregar explicitamente. Também carregaremos ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.