Re: [xml] XPath / LibXML question

"Aron Stansvik" <elvstone gmail com> wrote on 01/06/2006 15:19:06:

On 6/1/06, Alan_McCarthy scee net <Alan_McCarthy scee net> wrote:


I have a question about XPath and have been pointed in the direction of
this mailing list. Hope this is the correct place.

I have the following XPath:

/base/group/item[ att1=1]/instances/instance[ att2=2]

and when used on my XML document it returns multiple items, e.g.

/base[1]/group[1]/item[167]/instances[1]/instance[1] - result
/base[1]/group[1]/item[195]/instances[1]/instance[1] - result
/base[1]/group[1]/item[197]/instances[1]/instance[1] - result
/base[1]/group[1]/item[202]/instances[1]/instance[1] - result
/base[1]/group[1]/item[216]/instances[1]/instance[1] - result

In this particular instance however, I only need to find one of the
results, and it doesn't matter which one.
For CPU efficiency I would like to find a way to do that.
Does anyone know how I can achieve this, ideally by  modifying my
but if that is not possible, if there are parameters, or context set up
that could be done within LibXML to restrict it to one result.

You could use a predicate such as [position() = 1] to get the first
result. I don't know if this saves you anything performance-wise
though, one of the libxml2 hackers will have to answer that.

Best regards,
Aron Stansvik

Hi Aron,

I had played about with position(). Unless I am misunderstanding, The
position refers to that within XML data structure and not an index into the
XPath results. So position in the above instances are 167, 195, 197 etc...
These values would change if the XML data changed or I changed the
attributes within the XPath, I am hoping to find a generic XPath that could
cope with that



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