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I am trying to parse data encoded in HTML format. Example of the string I am trying to parse is:

Simplify the polynomial by combining like terms. <img src=\"/flx/math/inline/3x%2B12-11x%2B14\" class=\"x-math\" alt=\"3x+12-11x+14\" />

I want to get the text before <img and the text in alt=

Desired output:

Simplify the polynomial by combining like terms. 3x+12-11x+14

I tried scrapeR. 

y1 = scrape (str1)  # the above string is in str1 (as a vector)

I get the following error message

Error in which(value == defs) : 
  argument "code" is missing, with no default

Has anyone played with scrapeR. I am not sure what "code" refers to as it is an option and is not described in the manual. Just trying to see which default value is affecting this.

MrFlick
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user3763914
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  • the `scrape` function normally takes a URL as it's first unnamed parameter according to the documentation. What about `y1 = scrape(object="str1")`? – MrFlick Jun 28 '14 at 19:08
  • it accepts str1. y1=scrape(str1) produces the error. y1=scrape (object=str1) produces a different kind of error - unable to locate object str1. I think object=xxx is for objects with URLs etc. – user3763914 Jun 28 '14 at 19:15
  • It should be `y = scrape(object="str1")` not `y1 = scrape(object=str1)`. See the documentation at: http://www.rdocumentation.org/packages/scrapeR/functions/scrape – MrFlick Jun 28 '14 at 19:22
  • y = scrape(object="str1") puts the entire HTML wrapper in y. It now has etc. It is now a complete HTML file. (I was expecting the opposite result. (Appreciate your help). – user3763914 Jun 28 '14 at 19:59
  • @MrFlick, thanks for editing my original post and formatting it properly. (I will learn to do this). – user3763914 Jun 28 '14 at 20:00
  • But now what's the `class()` and `str()` of `y`? It should be some sort of iterable list i think now. – MrFlick Jun 28 '14 at 20:00

1 Answers1

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Here's one way to extract that information

str1<-"Simplify the polynomial by combining like terms. <img src=\"/flx/math/inline/3x%2B12-11x%2B14\" class=\"x-math\" alt=\"3x+12-11x+14\" />"

library(scrapeR)    
y<-scrape(object="str1")[[1]] #just get the first result

pretext <- sapply(xpathSApply(y, "//img/preceding::text()"), xmlValue)
alttext <- xpathSApply(y, "//img/@alt")

paste(pretext, alttext)
#[1] "Simplify the polynomial by combining like terms.  3x+12-11x+14"

The scrape() will return HTML/XML like document that you can work with using functions like xpathSApply to find nodes and extract values.

MrFlick
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  • Thank you very much. It works. Now I am going to figure out why it works! (thanks for putting me in the right direction) – user3763914 Jun 28 '14 at 21:24
  • found a good tutorial on webscraping using R. just posting it for future use. http://files.meetup.com/1503964/2010-06-24_WebScrapeIntro.pdf – user3763914 Jun 28 '14 at 21:30