How to return the diagonal line in table with xpath query?-CodePudding

given the following xml document:

<table>
  <tr><td>A</td>  <td>B</td>  <td>C</td></tr>
  <tr><td>1</td>  <td>2</td>  <td>3</td></tr>
  <tr><td>a</td>  <td>b</td>  <td>c</td></tr>
</table>

I am trying to write xpath query to get the diagonal line of the table.
I thought about the following query: //td[count(parent::td/preceding-sibling::tr) 1] But it's not working (it returns "No Match!" as result).

In the example above, the query need to return <td>A</td> <td>2</td> <td>c</td>

What is the problem with this query ?

CodePudding user response：

You are close. Just change

//td[count(parent::td/preceding-sibling::tr) 1]

//td[count(parent::tr/preceding-sibling::tr) 1]

//td[count(../preceding-sibling::tr) 1]

and your XPath will select

<td>A</td><td>2</td><td>c</td>

as desired.

preceding-sibling::tr selects all tr sibling elements before the context element. By counting those for the parent of a given td element, the whole XPath is able to select the diagonal td elements because the count of the preceding parent tr elements effectively gives the row number, and //td[ row number ] yields only those td elements where the column number (the n^th child td) equals the row number.

CodePudding user response：

First, I'm not sure why you're getting "No Match!" no match for the query in your question: the result should be <td>A</td> <td>1</td> <td>a</td> since the query resolves to 1 (because of the 1 at the end); there is no //td[parent::td] so the count is 0.

Since you are using xpath 3.0, you can try:

for $k in (1 to count(//tr)) return (//tr[$k]/td[$k])

It works on the table in the question.

See also