Xpath - how control every element value with others?

Question

EXAMPLE:
My XML:

<root>
    <a>
        <b>1</b>
        <b>1</b>
        <b>2</b>
    </a>
    <a>
        <b>1</b>
        <b>2</b>
    </a>
    <a>
        <b>1</b>
    </a>
</root>

A now, how to control that every "b" element has got only the same one value(not only "1")?
Is it possible? I found only, but it doesnt work: //a/b != ./b
I have no idea except some loop or count by value in element ... but it cant in xpath, or not?

Thanks for replies.

Given this sample XML, what do you want the XPath to return? — har07, Nov 01 '14 at 21:58
@har07 - probably true/false ... every b is the same or not. I know, it doesnt make a lot of sence here, in practice i need it for atribute. — MmM ..., Nov 01 '14 at 22:31
Only stating *"but it doesnt work"* without telling exactly why it does not work and not providing a code example is not good style to ask. Especially if you feel unsure with the correct technical wording, showing your code example can help a lot. — hakre, Nov 02 '14 at 10:51

score 2 · Accepted Answer · answered Nov 02 '14 at 11:01

To get the number of different values for all /*/a/b element nodes, you can count the distinct values of those elements:

count(/*/a/b[not(. = preceding::b)])

This expression will return 1 if there is one distinct value, 2 if two (as in your case) or 0 if there are no /*/a/b elements in the document.

PHP Example:

<?php

$buffer = <<<XML
<root>
    <a>
        <b>1</b>
        <b>1</b>
        <b>2</b>
    </a>
    <a>
        <b>1</b>
        <b>2</b>
    </a>
    <a>
        <b>1</b>
    </a>
</root>
XML;

$doc = new DOMDocument();
$doc->loadXML($buffer);
$xpath = new DOMXPath($doc);

echo $xpath->evaluate('count(/*/a/b[not(. = preceding::b)])');  # echoes 2

Very pretty, it should be faster i guess ... also very thank you. — MmM ..., Nov 02 '14 at 11:14

score 1 · Answer 2 · edited May 23 '17 at 12:06

If you mean by "control" that you actually want to have a Boolean return value telling you if all <b> elements have the same value you could use this expression:

count(/root/a/b[. != ../b]) = 0

It determines the <b>'s whose value is not like the values of other <b>'s. If the count is greater than 1 there is mismatch in at least one b so that the expression will be false. If the result set is empty the count will be 0 and the expression will be true.

This answer was inspired by How can I use XPath to find the minimum value of an attribute in a set of elements?.

Xpath - how control every element value with others?

2 Answers2