R help - Jul 2013 - [XML packages] how to get the sub-node according to the sub-node's attribute?

For example 

 fileName <- system.file("exampleData", "mtcars.xml",
package="XML")
 doc <- xmlTreeParse(fileName)
 r<-xmlRoot(doc)
 record<-r[["record"]]
 record
the result :
<record id="Mazda RX4">21.0   6 160.0 110 3.90 2.620 16.46  0  1
4    4</record>
but in the mecars.xml there are 32 sub-nodes called "record"

when I use xmlChildren function
c<-xmlChildren(r)[["record"]]


c is also like that
<record id="Mazda RX4">21.0   6 160.0 110 3.90 2.620 16.46  0  1
4    4</record>
just the first sub-node is the default  

My question is:
Is there a function that can get the sub-node according to the sub-node's
attribute ?
like that,in the mtcar.xml ,there is sub-node as follow:
<record id="Lotus Europa">        30.4   4  95.1 113 3.77 1.513
16.90  1  1    5    2</record>
I want to get the specific sub-node according to the attribute
"id="Lotus Europa".
Is there a simple function in the xml package?


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Liang He
Institute of Geographic Sciences and Natural resource research
Chinese Academy of Science,
No.11, Datun Road, Chaoyang District,
Beijing 100101, China
Email: xhl860728@163.com
Tel: +86(10) 6488 9513
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>My question is:
>Is there a function that can get the sub-node according to the
sub-node's attribute ?
>like that,in the mtcar.xml ,there is sub-node as follow:
><record id="Lotus Europa">        30.4   4  95.1 113 3.77
1.513 16.90  1  1    5    2</record>
>I want to get the specific sub-node according to the attribute
"id="Lotus Europa".
>Is there a simple function in the xml package?

Just use xpathSApply with brackets to specify the specific id...

 doc <- xmlParse(system.file("exampleData", "mtcars.xml",
package="XML"))

xpathSApply(doc, "//record[@id='Lotus Europa']", xmlValue)
[1] "        30.4   4  95.1 113 3.77 1.513 16.90  1  1    5    2"

#OR?
xpathSApply(doc, "//record[@id='Lotus Europa']")
getNodeSet(doc, "//record[@id='Lotus Europa']")

# And to list all Ids...

xpathSApply(doc, "//record", xmlGetAttr, "id")
 [1] "Mazda RX4"           "Mazda RX4 Wag"      
"Datsun 710"   .....

-- 

Chris Stubben

Los Alamos National Lab
Bioscience Division
MS M888
Los Alamos, NM 87545