如何使用R从javascript饼图中抓取网页数据？

Question

我有：

library(XML)

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

tables <- readHTMLTable(my_URL)

以上输出的只是位于页面顶部的表格。它看起来像饼图被忽略，事实是javascript解释它。是否有任何简单的解决方案来提取图表中的两个％数字？

看了RSelenium然而我得到了一些我无法找到任何解决方案的错误。

> 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 
> 

根据菲利普的回答，我提出了流动的解决方案：

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)

输出：

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

Answer 1

使用RSelenium

此解决方案适用于我使用Rselenium（使用Windows 7并在检查网页源之后）。请注意，我使用chromedriver.exe

library(RSelenium)
checkForServer(update = TRUE)

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

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

### Open 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")})

最后一个命令返回

[[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>"

您可以看到百分比数字出现在那里，可以轻松提取。

只使用普通的HTML

此外，还可以通过只读取html源来获取数据，因为数据已经包含在内。在源代码的某处你会发现：

<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],

];

这就是你要找的东西。数字在图中显示之前是圆整的。