R : Get attribute value from an XML

Question

I have a XML, see sample below

<params>
<param id='1'>BEN</param>
<param id='2'>DAN</param>
<param id='3'>RYE</param>
    <param id='3'>RYE</param>
    <param id='3'>RYE</param>
</params>

How can I get all the param with attribute id=3?

Below is what I have done so far : xmlinfile is the XML file

inxml = xmlTreeParse(xmlinfile, handlers=list("comment"=function(x,...){NULL}), asTree = TRUE)
xmlList = xmlToList(inxml);
params = xmlList$'params'

Thanks ahead.

plannapus · Accepted Answer · 2014-02-13 08:53:51Z

2

You need to use function xpathApply with argument xmlValue (to get the value, otherwise xmlAttrs to get the attribute). The path should be given in the following syntax :"//tag[@attribute='value']".

a <- xmlParse('<params>
<param id='1'>BEN</param>
<param id='2'>DAN</param>
<param id='3'>RYE</param>
    <param id='3'>RYE</param>
    <param id='3'>RYE</param>
</params>')
xpathApply(a,"//param[@id='3']",xmlValue)
[[1]]
[1] "RYE"

[[2]]
[1] "RYE"

[[3]]
[1] "RYE"

Similarly xpathSApply will gives you a vector of value when possible:

xpathSApply(a,"//param[@id='3']",xmlValue)
[1] "RYE" "RYE" "RYE"

answered Feb 13, 2014 at 8:53

plannapus

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lukeA · Accepted Answer · 2014-02-13 08:55:20Z

0

xmlinfile <- paste(readLines(n=7), collapse="\n")
<params>
  <param id='1'>BEN</param>
  <param id='2'>DAN</param>
  <param id='3'>RYE</param>
  <param id='3'>RYE</param>
  <param id='3'>RYE</param>
</params>
library(XML)
xpathApply(xmlParse(xmlinfile), "/params/param[@id='3']", xmlValue)  
# [[1]]
# [1] "RYE"
# 
# [[2]]
# [1] "RYE"
# 
# [[3]]
# [1] "RYE

answered Feb 13, 2014 at 8:55

lukeA

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