Xpath for choosing next sibling

Question

I have piece of HTML like this:

<dt>name</dt>
<dd>value</dd>
<dt>name2</dt>
<dd>value2</dd>

I want to find all places where the structure is incorrect, meaning there is no dd tag after dt tag.

I tried this:

//dt/following-sibling::dt

but this doesn't work. Any suggestions?

Solution 1

EDIT as noted by @Gaim, my original version failed to capture a terminal dt

string xml = @"
    <root>
    <dt>name</dt>
    <dd>value</dd>
    <dt>name2</dt>
    <dt>name3</dt>
    <dd>value3</dd>
    <dt>name4</dt>
    <dt>name5</dt>
    <dd>value5</dd>
    <dt>name6</dt>
    </root>
    ";

XmlDocument doc = new XmlDocument();
doc.LoadXml(xml);

XmlNodeList nodes = 
    doc.SelectNodes("//dt[not(following-sibling::*[1][self::dd])]");

foreach (XmlNode node in nodes)
{
    Console.WriteLine(node.OuterXml);
}

Console.ReadLine();

Output is those dt nodes that do not have a dd immediately following them:

<dt>name2</dt>
<dt>name4</dt>
<dt>name6</dt>

What we are doing here is saying:

//dt

All dt nodes, anywhere....

[not(following-sibling::*[1]

....such that it's not the case that their first following sibling (whatever it is called)....

[self::dd]]

...is called dd.

Solution 2

I am not sure that I understand you but there is my solution. This XPath matches ALL <dt> which are not followed by <dd> directly. So There is test structure

<xml>
  <dt>name</dt> <!-- match -->

  <dt>name2</dt>
  <dd>value2</dd>

  <dt>name</dt>
  <dd>value</dd>

  <dt>name2</dt>  <!-- match -->
</xml>

There is the XPath

//dt[ name( following-sibling::*[1] ) != 'dd' ]

or

//dt[  not( following-sibling::*[1]/self::dd ) ]

they do same thing

Comments

[Tomalak]

+1 -- The XPath expression can be molten down to //dt[following-sibling::*[1][self::dt]]

[Gaim]

@Tomalak Your XPath doesn't match all cases, look at my answer, you match only the first.

[AakashM]

+1 better than my original, which failed to capture a terminal dd-lacking dt

[Tomalak]

@Gaim: You are right. The not() approach is the correct one, I did not think about the case where a <dt> is last sibling.

[Frederic Bazin]

any idea how to deal when <dd> is missing e.g. <b>label1</b> value1 <br> <b>label2</b>value2 <br>...... ?

[Frederic Bazin]

see my new question at stackoverflow.com/questions/16745209/…