In theresagessler/learn2scrape: Learn To scrape web data in R

knitr::opts_chunk$set(
  # code chunk options
  echo = TRUE

  , eval = TRUE
  , warning = FALSE
  , message = FALSE
  , cached = FALSE
  , exercise = TRUE
  , exercise.completion = TRUE
  # figs
  , fig.align = "center"
  , fig.height = 4
  , fig.width = 5.5
  # , out.width = '50%'
)

library(learnr)

Introduction

Welcome to web scraping with learn2scrape! This R package offers an interactive way to learn web scraping in R by providing several self-contained tutorials. While these tutorials are designed to accompany our Automated Web data extraction course, you can also work through them on your own.

You can view all tutorials contained in the learn2scrape package by running the following code in your R console:

learnr::available_tutorials(package = "learn2scrape")

How to use tutorials

Each tutorial is a notebook with several sections.

Navigating

You can navigate through sections by clicking on items in the table of contents menu on the left-hand side of the tutorial or by clicking on the "Next Topic" button located at the end of a section's (at the bottom of your tutorial viewer/browser tab).

knitr::include_graphics("./images/menu.png")

Click "Continue" to learn more

What's in a section

Each tutorial section is usually a mix of text and code chunks.

• Text describes web scraping concepts, explains R code, or asks you to try out some code yourself.
• Code chunks show R code. They maybe maybe read-only or interactive.

You recognize interactive code chunks by top panel that includes a "Run Code" button.

knitr::include_graphics("./images/interactive-panel.png")

Caution: Beware of the "Start Over" button!

to the left of the "Run Code" button, there is a "Start Over" button. Clicking on this will reset the code in a given code chunk. So any changes you have made to the pre-defined R code will be lost if you click on this button!

This is even more important for the "Start Over" displayed in the left-hand tutorial panel below the table of content. Clicking on this button will reset the code for all interactive code chunks included in the tutorial! So all your work will be lost if you click on it.

Interactive code chunks

The most important thing about tutorials, and what makes them interactive, is that you can enter and run R code in interactive code chunks. So you cannot only execute the below code chunk interactively by clicking the "Run Code" button. You can also alter the R code in any way you want!

Try it yourself! Replace the string 'Hello world!' with some text of your choice and click "Run Code"

string <- 'Hello world!'
string

Compare this to the static (read-only) code chunk below. This just prints the code and the result of evaluating it below.

string <- 'Hello world!'
string

Interactive code chunks are forgetful!

One important thing to know about interactive code chunks is that they are independent from one another. So if you define an R objects or function in one code chunk, it won't be available in the following code chunks!

This is shown below. We first assing 1 to object one.

one <- 1

If we now try to evaluate it in the next code chunk, an error is raised.

Try it yourself! Click "Run Code" to trigger the error message.

one

This is the main difference of R tutorials to R Markdown documents or R scripts. Therefore, you will usually need to repeat code from previous exercises.

Viewing solutions

When we ask you to write some code on your own, we provide solutions. You can view solutions by clicking on the "‣" symbol below an interactive code chunk.

In the below example, your task would be to find the remaineder when 5 is divided by 2 (indicated by the "ToDo" comment). The solution can be viewed below this code chunk.

# ToDo: find the remainder when 5 is divided by 2

View the solution!

# ToDo: find the remainder when 5 is divided by 2
5 %% 2

theresagessler/learn2scrape documentation built on Dec. 23, 2021, 9:55 a.m.