[R] Example for parsing XML file?

[Brigid Mooney]

Thanks!  That helps a lot!

A quick follow-up question - I can't really tell what part of the
commands tell it to only look at the child nodes of <C>.  Is there any
way to also access the fields that are in the <C> heirarchy?  (ie the
S, D, C, and F)

I wouldn't necessarily want those repeated thousands of times in the
data frame, but C and F are useful reference points as they are
actually row numbers where specific events occurred.

Thanks again for all the help!
-Brigid



On Wed, May 20, 2009 at 5:16 PM, Duncan Temple Lang
<duncan at wald.ucdavis.edu> wrote:
> Hi Brigid.
>
> Here are a few commands that should do what you want:
>
> bri = xmlParse("myDataFile.xml")
>
> tmp =  t(xmlSApply(xmlRoot(bri), xmlAttrs))[, -1]
> dd = as.data.frame(tmp, stringsAsFactors = FALSE,
>                    row.names = 1:nrow(tmp))
>
> And then you can convert the columns to whatever types you want
> using regular R commands.
>
> The basic idea is that for each of the child nodes of C,
> i.e. the <T>'s, we want the character vector of attributes
> which we can get with xmlAttrs().
>
> Then we stack them together into a matrix, drop the "N"
> and then convert the result to a data frame, avoiding
> duplicate row names which are all "T".
>
> (BTW, make certain the '-' on the second line is not in the XML content.
>  I assume that came from bringing the text into mail.)
>
> HTH
>  D.
>
>
> Brigid Mooney wrote:
>>
>> Hi,
>>
>> I am trying to parse XML files and read them into R as a data frame,
>> but have been unable to find examples which I could apply
>> successfully.
>>
>> I'm afraid I don't know much about XML, which makes this all the more
>> difficult.  If someone could point me in the right direction to a
>> resource (preferably with an example or two), it would be greatly
>> appreciated.
>>
>> Here is a snippet from one of the XML files that I am looking to read,
>> and I am aiming to be able to get it into a data frame with columns N,
>> T, A, B, C as in the 2nd level of the heirarchy.
>>
>>  <?xml version="1.0" encoding="utf-8" ?>
>> - <C S="UnitA" D="1/3/2007" C="24745" F="24648">
>>  <T N="1" T="9:30:13 AM" A="30.05" B="29.85" C="30.05" />
>>  <T N="2" T="9:31:05 AM" A="29.89" B="29.78" C="30.05" />
>>  <T N="3" T="9:31:05 AM" A="29.9" B="29.86" C="29.87" />
>>  <T N="4" T="9:31:05 AM" A="29.86" B="29.86" C="29.87" />
>>  <T N="5" T="9:31:05 AM" A="29.89" B="29.86" C="29.87" />
>>  <T N="6" T="9:31:06 AM" A="29.89" B="29.85" C="29.86" />
>>  <T N="7" T="9:31:06 AM" A="29.89" B="29.85" C="29.86" />
>>  <T N="8" T="9:31:06 AM" A="29.89" B="29.85" C="29.86" />
>> </C>
>>
>> Thanks for any help or direction anyone can provide.
>>
>> As a point of reference, I am using R 2.8.1 and have loaded the XML
>> package.
>>
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>> and provide commented, minimal, self-contained, reproducible code.
>