Question
I've got a rather large XML file that I'm trying to parse using a C# application and the HtmlAgilityPack. The XML looks something like this:
...
<tr>
<td><b>ABC-123</b></td>
<td>15</td>
<td>4</td>
</tr>
<tr>
<td>AB-4-320</td>
<td>11</td>
<td>2</td>
</tr>
<tr>
<td><b>ABC-123</b></td>
<td>15</td>
<td>4</td>
</tr>
<tr>
<td>AB-4-320</td>
<td>11</td>
<td>2</td>
</tr>
<tr>
<td>CONTROLLER1</td>
<td>4</td>
<td>3</td>
</tr>
<td>CONTROLLER2</td>
<td>4</td>
<td>3</td>
</tr>
...
Basically a series of table rows and columns that repeats. I'm first doing a search for a controller by using:
string xPath = @"//tr/td[starts-with(.,'CONTROLLER2')]";
HtmlNodeCollection nodes = doc.DocumentNode.SelectNodes(xPath);
foreach (HtmlNode link in nodes) { ... }
Which returns the correct node. Now I want to search backwards (up) for the first (nearest) matching <td> node that starts with text "ABC":
string xPath = @link.XPath + @"/parent::tr/preceding-sibling::tr/td[starts-with(.,'ABC-')]";
This returns all matching nodes, not just the nearest one. When I attempted to add [1] to the end of this XPath string, it didn't seem to work and I've found no examples showing a predicate being used with an axes function like this. Or, more likely, I'm doing it wrong. Any suggestions?
Accepted Answer
You can use this XPath :
/parent::tr/preceding-sibling::tr[td[starts-with(.,'ABC-')]][1]/td[starts-with(.,'ABC-')]
That will search for nearest preceding <tr> that has child <td> starts with 'ABC-'. Then get that particular <td> element.
There are at least two approaches you can pick when using HtmlAgilityPack :
foreach (HtmlNode link in nodes)
{
//approach 1 : notice dot(.) at the beginning of the XPath
string xPath1 =
@"./parent::tr/preceding-sibling::tr[td[starts-with(.,'ABC-')]][1]/td[starts-with(.,'ABC-')]";
var n1 = node.SelectSingleNode(xPath1);
Console.WriteLine(n1.InnerHtml);
//approach 2 : appending to XPath of current link
string xPath2 =
@"/parent::tr/preceding-sibling::tr[td[starts-with(.,'ABC-')]][1]/td[starts-with(.,'ABC-')]";
var n2 = node.SelectSingleNode(link.XPath + xPath2);
Console.WriteLine(n2.InnerHtml);
}
Popular Answer
If you're able to use LINQ-to-XML instead of the HAP then this works:
var node = xml.Root.Elements("tr")
.TakeWhile(tr => !tr.Elements("td")
.Any(td => td.Value.StartsWith("CONTROLLER2")))
.SelectMany(tr => tr.Elements("td"))
.Where(td => td.Value.StartsWith("ABC-"))
.Last();
I got this result:
<td>
<b>ABC-123</b>
</td>
(Which I checked was the second matching node in your sample, not the first.)
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