first-steps-r.md

title	description	layout
Our R environment – the tidyverse	Ceci n'est pas une pipe	default

The tidyverse

• Within R, we're going to be using a set of packages that are part of what is called the "tidyverse". These used to be distinguished by a special symbol called a "pipe": %>%. The tidyverse pipe was so successful that the same functionality is now available in "base R" -- it just looks slightly differently: |>. How does the pipe work? It passes whetever is on the left side of the pipe as the first argument to the right side of the pipe:

• If we want to combine two strings, we can use paste0("Data", "Science). With a pipe, we can write the same thing as "Data" |> paste0("Science")
  • If this isn't completely clear, don't worry about it. The example later on make this very intuitive.

Setting up our R environment

Let's load up some helpful packages:

library(rvest) # the basic scraping library
library(dplyr) # a key part of the "tidyverse" that helps us manipulate Data
library(stringr) # a useful library that helps us clean up scraped text

You might need to install these packages if you don't have them.

R's webscraping commands

• Within R, webscraping is best done with a package called rvest

• Here are the functions you need to know:

  • read_html(url) will read a webpage into memory from the given url
  • html_node(page, css selector) will return the first node of a given page matched by the CSS selector.
  • html_nodes(page, css selector) works identically to html_node but selects all nodes matched by the css selector
  • html_text(node) extracts all text from a nodes
  • html_attr(node, attr) extracts the content of a given attribute from a node.
  • html_table(node) extracts an entire table into an R data frame

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