What is the process for utilizing R to extract data from a pie chart on a website that uses JavaScript?

Here's my code:

library(XML)

my_URL <- "http://www.velocitysharesetns.com/viix"

tables <- readHTMLTable(my_URL)

https://i.sstatic.net/Vadsw.png

The code above fetches only the table at the top of the webpage. The pie chart seems to be overlooked due to its Javascript nature. Any easy methods available to extract the two percentage values from the chart?

I've explored using RSelenium, but encountering some errors for which I haven't found solutions yet.

> RSelenium::startServer()
Error in if (file.exists(file) == FALSE) if (!missing(asText) && asText ==  : 
  argument is of length zero
In addition: Warning messages:
1: startServer is deprecated.
Users in future can find the function in file.path(find.package("RSelenium"), "example/serverUtils").
The sourcing/starting of a Selenium Server is a users responsiblity. 
Options include manually starting a server see vignette("RSelenium-basics", package = "RSelenium")
and running a docker container see  vignette("RSelenium-docker", package = "RSelenium") 
2: running command '"java" -jar "\\med-fs01/Home/Alex.Badoi/R/win-library/3.3/RSelenium/bin/selenium-server-standalone.jar" -log "\\med-fs01/Home/Alex.Badoi/R/win-library/3.3/RSelenium/bin/sellog.txt"' had status 127 
3: running command '"wmic" path win32_process get Caption,Processid,Commandline /format:htable' had status 44210 
>

Following Phillip's advice, here is my solution:

library(XML)



# extarct HTML

doc.html = htmlTreeParse('http://www.velocitysharesetns.com/viix',
                         useInternal = TRUE)


# convert to text

htmltxt <- paste(capture.output(doc.html, file=NULL), collapse="\n")

# get location of string

pos = regexpr('CBOE SHORT-TERM VIX FUTURE', htmltxt)

# extarct from "pos" to nchar to end of string 

keep = substr(htmltxt, pos, pos+98)

Output:

> keep
[1] "CBOE SHORT-TERM VIX FUTURE DEC 2016', 81.64],\n\n    ['CBOE SHORT-TERM VIX FUTURE JAN 2017', 18.36],\n"
javascriptrweb-scraping

Answer №1

RSelenium Method

I found success with this approach using RSelenium on Windows 7 after inspecting the webpage source. I specifically utilized chromedriver.exe for this solution.

library(RSelenium)
checkForServer(update = TRUE)

#### Chromedriver Implementation
startServer(args = c("-Dwebdriver.chrome.driver=C:/Stuff/Scripts/chromedriver.exe")) 

remDr <- remoteDriver(remoteServerAddr = "localhost", browserName="chrome", port=4444)

### Launch Chrome
remDr$open()

remDr$navigate("http://www.velocitysharesetns.com/viix")

b <- remDr$findElements(using="class name", value="jqplot-pie-series")

sapply(b, function(x){x$getElementAttribute("outerHTML")})

The final command provides the following output:

[[1]]
[1] "<div class=\"jqplot-pie-series jqplot-data-label\" style=\"position: absolute; left: 100px; top: 106px;\"><div style=\"color:white;font-weight:bold;\">82%</div></div>"

[[2]]
[1] "<div class=\"jqplot-pie-series jqplot-data-label\" style=\"position: absolute; left: 159px; top: 67px;\"><div style=\"color:white;font-weight:bold;\">18%</div></div>"

These results clearly display the percentage numbers which can be easily extracted.

Direct HTML Retrieval

Further data extraction can be achieved by analyzing the raw html source, as the necessary information is already present within it. You will likely locate the relevant details within the script below:

<script type="text/javascript" language="javascript">
$(document).ready(function(){
var data = [


['CBOE SHORT-TERM VIX FUTURE DEC 2016', 81.64],

['CBOE SHORT-TERM VIX FUTURE JAN 2017', 18.36],

];

This script contains the desired data, with the figures rounded before being displayed graphically.

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