Created by Keith McNulty on 26th July 2019
- Web Page Structure and Format
- Basic harvesting: The Billboard Hot 100 page
- Making scraping easy by automating tasks
Any webpage you visit has a particular, expected general structure. It usually consists of two types of code.
HTMLcode, which focuses on the appearance and format of a web page.XMLcode, which doesn’t look a lot different fromHTMLbut focuses more on managing data in a web page.
HTML code has an expected format and structure, to make it easy for
people to develop web pages. Here is an example of a simple HTML page:
<!DOCTYPE html>
<html>
<head>
<title>Page Title</title>
</head>
<body>
<h1>This is a Heading</h1>
<p>This is a paragraph.</p>
</body>
</html>
As you can see, the content is wrapped in tags like <head></head>,
<body></body>, <p></p>. These tags are pre-defined by the language
(you can only use the tags that HTML allows). Because HTML has a
more predictable structure, it is often easier to work with it and mine
it.
XML format and structure is less predictable. Although it looks very
similar to HTML, users can create their own named tags. Here is an
example:
<note>
<to>Keith</to>
<from>Steve</from>
<heading>Kudos</heading>
<body>Awesome work, dude!</body>
</note>
Tags like <to></to> and <from></from> are completely made up by me.
The fact that tags are not pre-defined makes XML a little harder to
mine and analyze. But it’s hard to get at some of the data on the web
without using XML.
To mine web data, it’s important that you can see the underlying code and understand how it relates to what you are seeing on the page. The best way to do this (in my opinion) is to use the Developer Tools that come with Google Chrome.
When you are viewing a web page in Chrome, simply used Ctrl+Shift+C in
Windows or Cmd+Option+C on a Mac to open up the Elements console where
you can see all the code underlying the page. This can look really
complex, but don’t worry. Here’s a photo of Google Chrome Developer open
on the Billboard Hot 100
page:
If you play around with the code in the Developer you will see that it has an embedded structure.
- At the highest level there is a
<html>tag. - At the second level there are
<head>and<body>tags. - Inside the
<body>of the page, different elements are often separated by<div>tags. - Many different types of tags continue to be embedded down to many nested levels
This is important because it means we can mine elements of a web page and treat them like lists in R. We often call a specific element of the page a node. So if we want to mine a specific node, we can capture its sub-nodes in a list. By doing so, this gives us the opportunity to apply the tidyverse when mining web pages. The process of mining data from the web is called scraping or harvesting.
The rvest and xml2 packages were designed to make it easier for
people working in R to harvest web data. Since xml2 is a required
package for rvest and the idea is that both packages work together,
you only need to install rvest. First, let’s ensure the packages we
need are installed and loaded:
if (!("rvest" %in% installed.packages())) {
install.packages("rvest")
}
if (!("dplyr" %in% installed.packages())) {
install.packages("dplyr")
}
library(rvest)## Loading required package: xml2
library(dplyr)##
## Attaching package: 'dplyr'
## The following objects are masked from 'package:stats':
##
## filter, lag
## The following objects are masked from 'package:base':
##
## intersect, setdiff, setequal, union
rvest and xml2 contain functions that allow us to read the code of a
web page, break it into a neat structure, and work with the pipe command
to efficiently find and extract specific pieces of information. Think of
it a bit like performing keyhole surgery on a webpage. Once you
understand what functions are available and what they do, it makes basic
web scraping very easy and can produce really powerful functionality.
We are going to use the example of mining the Billboard Hot 100 page at https://www.billboard.com/charts/hot-100. If you view this page, it’s pretty bling. There are videos popping up, images all over the place. But the basic point of the page is to show the current Hot 100 chart.
So let’s set ourselves the task of just harvesting the basic info from this page: Position Number, Artist, Song Title for the Hot 100.
First we load our packages and then we use the function read_html() to
capture the HTML code of the Billboard Hot 100 page.
hot100page <- "https://www.billboard.com/charts/hot-100"
hot100 <- read_html(hot100page)
hot100## {xml_document}
## <html class="" lang="">
## [1] <head>\n<meta http-equiv="Content-Type" content="text/html; charset= ...
## [2] <body class="chart-page chart-page- " data-trackcategory="Charts-The ...
str(hot100)## List of 2
## $ node:<externalptr>
## $ doc :<externalptr>
## - attr(*, "class")= chr [1:2] "xml_document" "xml_node"
The function has captured the entire content of the page in the form of
a special list-type document with two nodes <head> and <body>.
Almost always we are interested in the body of a web page. You can
select a node using html_node() and then see its child nodes using
html_children().
body_nodes <- hot100 %>%
html_node("body") %>%
html_children()
body_nodes## {xml_nodeset (20)}
## [1] <div class="header-wrapper ">\n<header id="site-header" class="site ...
## [2] <div class="site-header__placeholder"></div>
## [3] <main id="main" class="page-content"><div class="chart-detail-heade ...
## [4] <div class="ad_desktop dfp-ad" data-position="promo" data-sizes="[[ ...
## [5] <footer id="site-footer" class="site-footer"><div class="container ...
## [6] <script>\n window.CLARITY = window.CLARITY || [];\n</script>
## [7] <div class="ad_clarity" data-out-of-page="true" style="display: non ...
## [8] <script>\n CLARITY.push({\n use: ['ads', 'cookies', 'head ...
## [9] <script type="text/javascript" src="https://assets.billboard.com/as ...
## [10] <script type="text/javascript" src="https://assets.billboard.com/as ...
## [11] <script type="text/javascript" src="https://assets.billboard.com/as ...
## [12] <script type="text/javascript" src="https://assets.billboard.com/as ...
## [13] <script type="text/javascript" src="https://assets.billboard.com/as ...
## [14] <script type="text/javascript">\n\tvar _sf_async_config={};\n\t/** ...
## [15] <script class="kxct" data-id="JsVUOKRj" data-timing="async" data-ve ...
## [16] <script class="kxint" type="text/javascript">\n window.Krux||((K ...
## [17] <script data-src="//platform.instagram.com/en_US/embeds.js"></script>
## [18] <script data-src="//platform.twitter.com/widgets.js"></script>
## [19] <div id="fb-root"></div>
## [20] <script type="text/javascript">\n PGM.createScriptTag("//connect ...
If we want, we can go one level deeper, to see the nodes inside the nodes. In this way, we can just continue to pipe deeper into the code:
body_nodes %>%
html_children()## {xml_nodeset (12)}
## [1] <header id="site-header" class="site-header " role="banner"><div cl ...
## [2] <div class="header-wrapper__secondary-header">\n<nav class="site-he ...
## [3] <div class="chart-detail-header">\n<div class="chart-detail-header_ ...
## [4] <div class="ad-container leaderboard leaderboard--top">\n<div class ...
## [5] <div class="container chart-container container--xxlight-grey conta ...
## [6] <div class="chart-list__expanded-header">\n<div class="chart-list__ ...
## [7] <div id="dateSearchModal" class="date-search-modal" data-visible="f ...
## [8] <div class="ad-holder ad-holder--footer">\n<div class="ad_desktop d ...
## [9] <div class="container footer-content">\n<div class="cover-image">\n ...
## [10] <div class="container">\n<p class="copyright__paragraph">© 2019 Bil ...
## [11] <div class="container">\n<p class="station-identification">\nBillbo ...
## [12] <div class="container">\n<div class="ad_desktop dfp-ad dfp-ad-adhes ...
So we could mess around with the functions above for a long time, but
might find it hard to work out where exactly this chart data is. We can
use Chrome Developer to tell us where we can find the data in the code,
and then we can use rvest to harvest out the data.
If you run your mouse over the code in the Developer you will see that the elements of the page that the code refers to are highlighted in the browser. You can click to expand embedded nodes to get to more specific parts of the page. You can watch the video I added to this repo to see how I progressively drill down the code to find the precise nodes that contain the details of each chart entry.
What we see is that each chart entry appears to be in a <div> tag with
the class name chart-list-item and the div tag seems to have
attributes that we are interested in, namely data-rank, data-artist,
data-title.
Now we can use the function xml_find_all() to find all <div> nodes
in the body of the document that have a class name containing
chart-list-item. xml_find_all() accepts xpath syntax. You can
learn more about xpath syntax
here:
chart_items <- hot100 %>%
html_node("body") %>%
xml_find_all("//div[contains(@class, 'chart-list-item')]")
chart_items## {xml_nodeset (2595)}
## [1] <div class="chart-list-item__expanded-header">\n<div class="chart-v ...
## [2] <div class="chart-list-item " data-rank="1" data-artist="Lil Nas X ...
## [3] <div class="chart-list-item__first-row chart-list-item__cursor-poin ...
## [4] <div class="chart-list-item__position ">\n<div class="chart-list-it ...
## [5] <div class="chart-list-item__rank ">\n1\n</div>
## [6] <div class="chart-list-item__award">\n<i class="fa fa-dot-circle-o" ...
## [7] <div class="chart-list-item__image-wrapper">\n<div class="chart-lis ...
## [8] <div class="chart-list-item__video-play-overlay">\n<img class="play ...
## [9] <div class="chart-list-item__trend-icon">\n</div>
## [10] <div class="chart-list-item__text-wrapper">\n<div class="chart-list ...
## [11] <div class="chart-list-item__text chart-list-item__text--has-video" ...
## [12] <div class="chart-list-item__title">\n<span class="chart-list-item_ ...
## [13] <div class="chart-list-item__artist">\nLil Nas X Featuring Billy Ra ...
## [14] <div class="chart-list-item__lyrics">\n<a href="https://www.billboa ...
## [15] <div class="chart-list-item__video-icon-wrapper">\n<div class="char ...
## [16] <div class="chart-list-item__video-icon chart-list-item__video--pla ...
## [17] <div class="chart-list-item__chevron-wrapper">\n <i class="fa fa-ch ...
## [18] <div class="chart-list-item__extra-info">\n<div class="chart-list-i ...
## [19] <div class="chart-list-item__extra-info-shadow"></div>
## [20] <div class="chart-list-item__expanded-header">\n<div class="chart-v ...
## ...
This looks like there’s a lot of nodes that have our search string in
them, but Node 2 looks interesting - let’s take a closer look at its
attributes using the function xml_attrs().
chart_items[2] %>%
xml_attrs()## [[1]]
## class
## "chart-list-item "
## data-rank
## "1"
## data-artist
## "Lil Nas X Featuring Billy Ray Cyrus"
## data-title
## "Old Town Road"
## data-has-content
## "true"
Now that looks like what we want. Nice! So it looks like we are after
<div> nodes with the class 'chart-list-item ' (note the two spaces
at the end.) You’ll see that these <div> nodes have the attributes we
need, and we can draw them down individually using the xml_attr()
function:
title <- hot100 %>%
html_node("body") %>%
xml_find_all("//div[contains(@class, 'chart-list-item ')]") %>%
xml_attr("data-title")
title %>% head(10)## [1] "Old Town Road"
## [2] "Bad Guy"
## [3] "I Don't Care"
## [4] "Senorita"
## [5] "Talk"
## [6] "Truth Hurts"
## [7] "Goodbyes"
## [8] "Sucker"
## [9] "Sunflower (Spider-Man: Into The Spider-Verse)"
## [10] "No Guidance"
That’s the Billboard Hot 100 Top 10! Nice! Now we can easy draw down the other two attributes we want and combine them all into a neat dataframe.
rank <- hot100 %>%
html_node("body") %>%
xml_find_all("//div[contains(@class, 'chart-list-item ')]") %>%
xml_attr('data-rank')
artist <- hot100 %>%
html_node("body") %>%
xml_find_all("//div[contains(@class, 'chart-list-item ')]") %>%
xml_attr('data-artist')
chart_df <- data.frame(rank, artist, title)
knitr::kable(
chart_df %>% head(10)
)| rank | artist | title |
|---|---|---|
| 1 | Lil Nas X Featuring Billy Ray Cyrus | Old Town Road |
| 2 | Billie Eilish | Bad Guy |
| 3 | Ed Sheeran & Justin Bieber | I Don’t Care |
| 4 | Shawn Mendes & Camila Cabello | Senorita |
| 5 | Khalid | Talk |
| 6 | Lizzo | Truth Hurts |
| 7 | Post Malone Featuring Young Thug | Goodbyes |
| 8 | Jonas Brothers | Sucker |
| 9 | Post Malone & Swae Lee | Sunflower (Spider-Man: Into The Spider-Verse) |
| 10 | Chris Brown Featuring Drake | No Guidance |
Generally we don’t just scrape a single webpage for fun. We are usually scraping because there is information that we need on a large scale or on a regular basis. Therefore, once you have worked out how to scrape this information, you’ll need to set things up in a way that it is easy to obtain it in the future. Writing functions is often a good way of doing this.
If you take a look around the billboard site, you’ll see that you can basically look up any chart at any date in history by simply inserting the chart name and date at the appropriate point in the URL. For example, to see the Billboard 200 on 21st July 1972 you would navigate to https://www.billboard.com/charts/billboard-200/1972-07-21.
Since this will always produce a webpage in exactly the same structure as the one we just scraped, we can now create quite a powerful function that accepts a chart name, date and set of ranks, and returns the entries for that chart on that date in those ranks.
#' Get billboard chart entries from history
#'
#' @param date date in the form YYYY-MM-DD
#' @param positions numeric vector
#' @param type character string of chart type (as per billboard.com URLs)
#' @return a dataframe of rank, artist, title
#' @examples get_chart(date = "1972-11-02", positions = c(1:100), type = "billboard-200")
get_chart <- function(date = Sys.Date(), positions = c(1:10), type = "hot-100") {
# get url from input and read html
input <- paste0("https://www.billboard.com/charts/", type, "/", date)
chart_page <- xml2::read_html(input)
# scrape data
chart <- chart_page %>%
rvest::html_nodes('body') %>%
xml2::xml_find_all("//div[contains(@class, 'chart-list-item ')]")
rank <- chart %>%
xml2::xml_attr('data-rank')
artist <- chart %>%
xml2::xml_attr('data-artist')
title <- chart %>%
xml2::xml_attr('data-title')
# create dataframe, remove nas and return result
chart_df <- data.frame(rank, artist, title)
chart_df <- chart_df %>%
dplyr::filter(!is.na(rank), rank %in% positions)
chart_df
}Now let’s test our function by looking up the Top 10 singles from 20th January 1975:
test1 <- get_chart(date = "1975-01-20", positions = 1:10, type = "hot-100")
knitr::kable(test1)| rank | artist | title |
|---|---|---|
| 1 | Carpenters | Please Mr. Postman |
| 2 | Neil Sedaka | Laughter In The Rain |
| 3 | Barry Manilow | Mandy |
| 4 | Ohio Players | Fire |
| 5 | Stevie Wonder | Boogie On Reggae Woman |
| 6 | Linda Ronstadt | You’re No Good |
| 7 | Paul Anka with Odia Coates | One Man Woman/One Woman Man |
| 8 | Donny & Marie Osmond | Morning Side Of The Mountain |
| 9 | Gloria Gaynor | Never Can Say Goodbye |
| 10 | AWB | Pick Up The Pieces |
Similarly, we can create a function get_eurovision() to scrape the
results of any Eurovision Song
Contest since
1957. I will source this function from inside this repo and then grab
the 1974 contest results:
source("eurovision_scraping.R")
eurovision_1974 <- get_eurovision(1974)
knitr::kable(eurovision_1974)| Country | Artist | Song | Language[9] | Place | Points |
|---|---|---|---|---|---|
| Sweden | ABBA | “Waterloo” | English | 1 | 24 |
| Italy | Gigliola Cinquetti | “Sì” | Italian | 2 | 18 |
| Netherlands | Mouth & MacNeal | “I See a Star” | English | 3 | 15 |
| United Kingdom | Olivia Newton-John | “Long Live Love” | English | 4 | 14 |
| Luxembourg | Ireen Sheer | “Bye Bye I Love You” | Frencha | 4 | 14 |
| Monaco | Romuald | “Celui qui reste et celui qui s’en va” | French | 4 | 14 |
| Israel | Kaveret | “Natati La Khayay” (נתתי לה חיי) | Hebrew | 7 | 11 |
| Ireland | Tina Reynolds | “Cross Your Heart” | English | 7 | 11 |
| Spain | Peret | “Canta y sé feliz” | Spanish | 9 | 10 |
| Belgium | Jacques Hustin | “Fleur de liberté” | French | 9 | 10 |
| Greece | Marinella | “Krasi, thalassa ke t’ agori mou”(Κρασί, θάλασσα και τ’ αγόρι μου) | Greek | 11 | 7 |
| Yugoslavia | Korni Grupa | “Generacija ’42” (Генерација ’42) | Serbian | 12 | 6 |
| Finland | Carita | “Keep Me Warm” | English | 13 | 4 |
| Norway | Anne-Karine Strøm feat. Bendik Singers | “The First Day of Love” | English | 14 | 3 |
| Germany | Cindy & Bert | “Die Sommermelodie” | German | 14 | 3 |
| Switzerland | Piera Martell | “Mein Ruf nach dir” | German | 14 | 3 |
| Portugal | Paulo de Carvalho | “E depois do adeus” | Portuguese | 14 | 3 |
Recently I thought it might be useful to have a package that generated random facts for people. This could be helpful for scripts or apps that take a long time to execute, where you could occasionally display random facts to keep people interested.
The Wikipedia Main Page has three predictable sections which can be reliably scraped. So I used them to create three functions:
wiki_didyouknow()which takes random facts from the ‘Did you know…’ sectionwiki_onthisday()which takes random facts from the ‘On this day…’ sectionwiki_inthenews()which takes random facts from the ‘In the news…’ section
A fourth function wiki_randomfact() executes one of the above three
functions at random.
I packaged this into a package called wikifacts which can be installed
from github. Here’s some examples of the functions at work:
library(devtools)
devtools::install_github("keithmcnulty/wikifacts")## Skipping install of 'wikifacts' from a github remote, the SHA1 (50ef374c) has not changed since last install.
## Use `force = TRUE` to force installation
library(wikifacts)
wiki_didyouknow()## Did you know that Joe Biden prefers the Chevrolet Corvette, but Joe Biden prefers the Pontiac Trans Am? (Courtesy of Wikipedia)
wiki_onthisday()## Did you know that on this day in 2009 – The militant Islamist group Boko Haram launched an attack on a Nigeria Police Force station, sparking violence across several states in northeastern Nigeria, leaving more than 1,000 people dead. (Courtesy of Wikipedia)