CODEWITHSUNDEEP
xpath
Wilfred Knievel
Wilfred Knievel

Reputation: 3245

Find position of a node using XPath

Anyone know how to get the position of a node using XPath?

Say I have the following xml:

<a>
    <b>zyx</b>
    <b>wvu</b>
    <b>tsr</b>
    <b>qpo</b>
</a>

I can use the following xpath query to select the third <b> node (<b>tsr</b>):

a/b[.='tsr']

Which is all well and good but I want to return the ordinal position of that node, something like:

a/b[.='tsr']/position()

(but a bit more working!)

Is it even possible?

edit: Forgot to mention am using .net 2 so it's xpath 1.0!

Update: Ended up using James Sulak's excellent answer. For those that are interested here's my implementation in C#:

int position = doc.SelectNodes("a/b[.='tsr']/preceding-sibling::b").Count + 1;

// Check the node actually exists
if (position > 1 || doc.SelectSingleNode("a/b[.='tsr']") != null)
{
    Console.WriteLine("Found at position = {0}", position);
}

Upvotes: 93

Views: 127653

Answers (8)

CroWell
CroWell

Reputation: 616

If you ever upgrade to XPath 2.0, note that it provides function index-of, it solves problem this way:

index-of(//b, //b[.='tsr'])

Where:

  • 1st parameter is sequence for searching
  • 2nd is what to search

Upvotes: 6

Claus Jensen
Claus Jensen

Reputation: 31

Just a note to the answer done by James Sulak.

If you want to take into consideration that the node may not exist and want to keep it purely XPATH, then try the following that will return 0 if the node does not exist.

count(a/b[.='tsr']/preceding-sibling::*)+number(boolean(a/b[.='tsr']))

Upvotes: 3

James Sulak
James Sulak

Reputation: 32447

Try:

count(a/b[.='tsr']/preceding-sibling::*)+1.

Upvotes: 107

user414661
user414661

Reputation: 1042

I realize that the post is ancient.. but..

replace'ing the asterisk with the nodename would give you better results

count(a/b[.='tsr']/preceding::a)+1.

instead of

count(a/b[.='tsr']/preceding::*)+1.

Upvotes: 9

Damien
Damien

Reputation: 2254

Unlike stated previously 'preceding-sibling' is really the axis to use, not 'preceding' which does something completely different, it selects everything in the document that is before the start tag of the current node. (see http://www.w3schools.com/xpath/xpath_axes.asp)

Upvotes: 3

geoffc
geoffc

Reputation: 4100

I do a lot of Novell Identity Manager stuff, and XPATH in that context looks a little different.

Assume the value you are looking for is in a string variable, called TARGET, then the XPATH would be:

count(attr/value[.='$TARGET']/preceding-sibling::*)+1

Additionally it was pointed out that to save a few characters of space, the following would work as well:

count(attr/value[.='$TARGET']/preceding::*) + 1

I also posted a prettier version of this at Novell's Cool Solutions: Using XPATH to get the position node

Upvotes: 0

Andrew Cox
Andrew Cox

Reputation: 10988

The problem is that the position of the node doesn't mean much without a context.

The following code will give you the location of the node in its parent child nodes

using System;
using System.Xml;

public class XpathFinder
{
    public static void Main(string[] args)
    {
        XmlDocument xmldoc = new XmlDocument();
        xmldoc.Load(args[0]);
        foreach ( XmlNode xn in xmldoc.SelectNodes(args[1]) )
        {
            for (int i = 0; i < xn.ParentNode.ChildNodes.Count; i++)
            {
                if ( xn.ParentNode.ChildNodes[i].Equals( xn ) )
                {
                    Console.Out.WriteLine( i );
                    break;
                }
            }
        }
    }
}

Upvotes: 0

Steven Huwig
Steven Huwig

Reputation: 20784

You can do this with XSLT but I'm not sure about straight XPath.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" encoding="utf-8" indent="yes" 
              omit-xml-declaration="yes"/>
  <xsl:template match="a/*[text()='tsr']">
    <xsl:number value-of="position()"/>
  </xsl:template>
  <xsl:template match="text()"/>
</xsl:stylesheet>

Upvotes: 9

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