I was told that the following are not the same:
a[1][#attr="foo"]
a[#attr="foo"][1]
Can someone explain why that is the case?
Think of XPath expressions as defining a result set1 - a set of nodes that fulfil all the requirements stated in the XPath expression. The predicates of XPath expressions (the parts inside []) either have no effect on the result set or they incrementally narrow it.
Put another way, in the following expression:
//xyz[#abc="yes"]
[#abc="yes"] reduces the result set defined to the left of it, by //xyz.
Note that, as Michael Kay has suggested, all that is said below only applies to XPath expressions with at least one positional predicate. Positional predicates are either a number: [1] or evaluate to a number, or contain position() or last().
If no positional predicate is present, the order of predicates in XPath expressions is not significant.
Consider the following simple input document:
<root>
<a attr="other"/>
<a attr="foo"/>
<a attr="other"/>
<a attr="foo"/>
</root>
As you can see, a[#attr = 'foo'] is not the first child element of root. If we apply
//a[1]
to this document, this will of course result in
<a attr="other"/>
Now, crucially, if we add another predicate to the expression, like so:
//a[1][#attr="foo"]
Then, [#attr="foo"] can only influence the result set defined by //a[1] already. In this result set, there is no a[#attr="foo"] - and the final result is empty.
On the other hand, if we start out with
//a[#attr="foo"]
the result will be
<a attr="foo"/>
-----------------------
<a attr="foo"/>
and in this case, if we add a second predicate:
//a[#attr="foo"][1]
the second predicate [1] can narrow down the result set of //a[#attr="foo"] to only contain the first of those nodes.
If you know XSLT, you might find an XSLT (and XPath 2.0) proof of this helpful:
<?xml version="1.0" encoding="UTF-8" ?>
<xsl:transform xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="2.0">
<xsl:output method="xml" omit-xml-declaration="yes" encoding="UTF-8" indent="yes" />
<xsl:template match="/">
<result1>
<xsl:copy-of select="//a[1][#attr='foo']"/>
</result1>
<result2>
<xsl:copy-of select="//a[#attr='foo'][1]"/>
</result2>
</xsl:template>
</xsl:transform>
And the result will be
<result1/>
<result2>
<a attr="foo"/>
</result2>
1 Technically speaking, only XPath 1.0 calls this result a node-set. In XPath 2.0, all sets have become true sequences of nodes.
Related
I use 'XPath', how I can simulate split method?
I read documentation and I know that XPath version 1.0 not have this method.
I have document contains this tags:
<TestCategoryModule>
<ItemCategories>
<![CDATA[Birthday Travel,Travel]]>
</ItemCategories>
</TestCategoryModule>
<TestCategoryModule2>
<ItemCategories>
<![CDATA[Travel]]>
</ItemCategories>
</TestCategoryModule2>
I want filter item by 'ItemCategories', but when I filtered by world 'Travel', return 2 item. I use this filter "ItemCategories[contains(text(), 'Travel')]".
I want that I filter by "Travel" return only second item. How can do it?
Use:
/*/*/*[contains(concat(',', ., ','), ',Travel,')]
Here is XSLT-based verification:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:template match="/">
<xsl:copy-of select=
"/*/*/*[contains(concat(',', ., ','), ',Travel,')]"/>
</xsl:template>
</xsl:stylesheet>
When this transformation is applied on this XML document (essentially the provided XML fragment, extended with one more test case and made a well-formed XML document:
<t>
<TestCategoryModule>
<ItemCategories>Birthday Travel,Travel</ItemCategories>
</TestCategoryModule>
<TestCategoryModule2>
<ItemCategories>Birthday Travel</ItemCategories>
</TestCategoryModule2>
<TestCategoryModule2>
<ItemCategories>Travel</ItemCategories>
</TestCategoryModule2>
</t>
The wanted, correct result is produced:
<ItemCategories>Birthday Travel,Travel</ItemCategories>
<ItemCategories>Travel</ItemCategories>
I was a little wrong, or poorly described problumu. The problem is that the categories are stored as a string. I have three items, the first one contains categories: (Birthday Travel,Travel), second: (Birthday Travel), third: (Travel). When I request filtering for the word "Travel", I need to get the first and third items, but I get all three items, because all items contain world "Travel".
You actually don't need split() for the problem that you've described. If you want to match Travel but not Travel,Travel you want = instead of contains(). To deal with the whitespace around your CDATA sections, wrap it in normalize-space().
All put together, try ItemCategories[normalize-space(text()) = 'Travel'].
Originally: **How to apply XPath query to a XML variable typed as element()* **
I wish to apply XPath queries to a variable passed to a function in XSLT 2.0.
Saxon returns this error:
Type error at char 6 in xsl:value-of/#select on line 13 column 50 of stackoverflow_test.xslt:
XTTE0780: Required item type of result of call to f:test is element(); supplied value has item type text()
This skeleton of a program is simplified but, by the end of its development, it is meant to pass an element tree to multiple XSLT functions. Each function will extract certain statistics and create reports from the tree.
When I say apply XPath queries, I mean I wish to have the query consider the base element in the variable... if you please... as if I could write {count(doc("My XSLT tree/element variable")/a[1])}.
Using Saxon HE 9.7.0.5.
<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:f="f:f">
<xsl:template match="/root">
<xsl:variable name="first" as="element()*">
<xsl:copy-of select="(./a[1])" />
</xsl:variable>
<html>
<xsl:copy-of select="f:test($first)" />
</html>
</xsl:template>
<xsl:function name="f:test" as="element()*">
<xsl:param name="frstElem" as="element()*" />
<xsl:value-of select="count($frstElem/a)" />
<!-- or any XPath expression -->
</xsl:function>
</xsl:stylesheet>
Some example data
<root>
<a>
<b>
<c>hi</c>
</b>
</a>
<a>
<b>
<c>hi</c>
</b>
</a>
</root>
Possibly related question: How to apply xpath in xsl:param on xml passed as input to xml
What you are doing is perfectly correct, except that you have passed an a element to the function, and the function is looking for an a child of this element, and with your sample data this will return an empty sequence.
If you want f:test() to return the number of a elements in the sequence that is the value of $frstElem, you can use something like
<xsl:value-of select="count($frstElem/self::a)" />
instead of using the (implicit) child:: axis.
Given markup like:
<p>
<code>foo</code><code>bar</code>
<code>jim</code> and then <code>jam</code>
</p>
I need to select the first three <code>—but not the last. The logic is "Select all code elements that have a preceding-or-following-sibling-element that is also a code, unless there exist one or more text nodes with non-whitespace content between them.
Given that I am using Nokogiri (which uses libxml2) I can only use XPath 1.0 expressions.
Although a tricky XPath expression is desired, Ruby code/iterations to perform the same on a Nokogiri document are also acceptable.
Note that the CSS adjacent sibling selector ignores non-element nodes, and so selecting nokodoc.css('code + code') will incorrectly select the last <code> block.
Nokogiri.XML('<r><a/><b/> and <c/></r>').css('* + *').map(&:name)
#=> ["b", "c"]
Edit: More test cases, for clarity:
<section><ul>
<li>Go to <code>N</code> and
then <code>Y</code><code>Y</code><code>Y</code>.
</li>
<li>If you see <code>N</code> or <code>N</code> then…</li>
</ul>
<p>Elsewhere there might be: <code>N</code></p>
<p><code>N</code> across parents.</p>
<p>Then: <code>Y</code> <code>Y</code><code>Y</code> and <code>N</code>.</p>
<p><code>N</code><br/><code>N</code> elements interrupt, too.</p>
</section>
All the Y above should be selected. None of the N should be selected. The content of the <code> are used only to indicate which should be selected: you may not use the content to determine whether or not to select an element.
The context elements in which the <code> appear are irrelevant. They may appear in <li>, they may appear in <p>, they may appear in something else.
I want to select all the consecutive runs of <code> at once. It is not a mistake that there is a space character in the middle of one of sets of Y.
Use:
//code
[preceding-sibling::node()[1][self::code]
or
preceding-sibling::node()[1]
[self::text()[not(normalize-space())]]
and
preceding-sibling::node()[2][self::code]
or
following-sibling::node()[1][self::code]
or
following-sibling::node()[1]
[self::text()[not(normalize-space())]]
and
following-sibling::node()[2][self::code]
]
XSLT - based verification:
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:template match="/">
<xsl:copy-of select=
"//code
[preceding-sibling::node()[1][self::code]
or
preceding-sibling::node()[1]
[self::text()[not(normalize-space())]]
and
preceding-sibling::node()[2][self::code]
or
following-sibling::node()[1][self::code]
or
following-sibling::node()[1]
[self::text()[not(normalize-space())]]
and
following-sibling::node()[2][self::code]
]"/>
</xsl:template>
</xsl:stylesheet>
When this transformation is applied on the provided XML document:
<section><ul>
<li>Go to <code>N</code> and
then <code>Y</code><code>Y</code><code>Y</code>.
</li>
<li>If you see <code>N</code> or <code>N</code> then…</li>
</ul>
<p>Elsewhere there might be: <code>N</code></p>
<p><code>N</code> across parents.</p>
<p>Then: <code>Y</code> <code>Y</code><code>Y</code> and <code>N</code>.</p>
<p><code>N</code><br/><code>N</code> elements interrupt, too.</p>
</section>
the contained XPath expression is evaluated and the selected nodes are copied to the output:
<code>Y</code>
<code>Y</code>
<code>Y</code>
<code>Y</code>
<code>Y</code>
<code>Y</code>
//code[
(
following-sibling::node()[1][self::code]
or (
following-sibling::node()[1][self::text() and normalize-space() = ""]
and
following-sibling::node()[2][self::code]
)
)
or (
preceding-sibling::node()[1][self::code]
or (
preceding-sibling::node()[1][self::text() and normalize-space() = ""]
and
preceding-sibling::node()[2][self::code]
)
)
]
I think this does what you want, though I won’t claim you’d actually want to use it.
I’m assuming text nodes are always merged together so that there won’t be two adjacent to each other, which I believe is generally the case, but might not be if you’re doing DOM manipulations beforehand. I’ve also assumed that there won’t be any other elements between code elements, or that if there are they prevent selection like non-whitespace text.
I think this is what you want:
/p/code[not(preceding-sibling::text()[not(normalize-space(.)="")])]
I have an XML document as follows:
<objects>
<object uid="0" />
<object uid="1" />
<object uid="2" />
</objects>
I can select multiple elements using the following query:
doc.xpath("//object[#uid=2 or #uid=0 or #uid=1]")
But this returns the elements in the same order they're declared in the XML document (uid=0, uid=1, uid=2) and I want the results in the same order as I perform the XPath query (uid=2, uid=0, uid=1).
I'm unsure if this is possible with XPath alone, and have looked into XSLT sorting, but I haven't found an example that explains how I could achieve this.
I'm working in Ruby with the Nokogiri library.
There is no way in XPath 1.0 to specify the order of the selected nodes.
XPath 2.0 allows a sequence of nodes with any specific order:
//object[#uid=2], //object[#uid=1]
evaluates to a sequence in which all object items with #uid=2 precede all object items with #uid=1
If one doesn't have anXPath 2.0 engine available, it is still possible to use XSLT in order to output nodes in any desired order.
In this specific case the sequence of the following XSLT instructions:
<xsl:copy-of select="//object[#uid=2]"/>
<xsl:copy-of select="//object[#uid=1]"/>
produces the desired output:
<object uid="2" /><object uid="1" />
I am assuming you are using XPath 1.0. The W3C spec says:
The primary syntactic construct in XPath is the expression. An expression matches the production Expr. An expression is evaluated to yield an object, which has one of the following four basic types:
* node-set (an unordered collection of nodes without duplicates)
* boolean (true or false)
* number (a floating-point number)
* string (a sequence of UCS characters)
So I don't think you can re-order simply using XPath. (The rest of the spec defines document order and reverse document order, so if the latter does what you want you can get it using the appropriate axis (e.g. preceding).
In XSLT you can use <xsl:sort> using the name() of the attribute. The XSLT FAQ is very good and you should find an answer there.
An XSLT example:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:param name="pSequence" select="'2 1'"/>
<xsl:template match="objects">
<xsl:for-each select="object[contains(concat(' ',$pSequence,' '),
concat(' ',#uid,' '))]">
<xsl:sort select="substring-before(concat(' ',$pSequence,' '),
concat(' ',#uid,' '))"/>
<xsl:copy-of select="."/>
</xsl:for-each>
</xsl:template>
</xsl:stylesheet>
Output:
<object uid="2" /><object uid="1" />
I don't think there is a way to do it in xpath but if you wish to switch to XSLT you can use the xsl:sort tag:
<xsl:for-each select="//object[#uid=1 or #uid=2]">
<xsl:sort: select="#uid" data-type="number" />
{insert new logic here}
</xsl:for-each>
more complete info here:
http://www.w3schools.com/xsl/el_sort.asp
This is how I'd do it in Nokogiri:
require 'nokogiri'
xml = '<objects><object uid="0" /><object uid="1" /><object uid="2" /></objects>'
doc = Nokogiri::XML(xml)
objects_by_uid = doc.search('//object[#uid="2" or #uid="1"]').sort_by { |n| n['uid'].to_i }.reverse
puts objects_by_uid
Running that outputs:
<object uid="2"/>
<object uid="1"/>
An alternative to the search would be:
objects_by_uid = doc.search('//object[#uid="2" or #uid="1"]').sort { |a,b| b['uid'].to_i <=> a['uid'].to_i }
if you don't like using sort_by with the reverse.
XPath is useful for locating and retrieving the nodes but often the filtering we want to do gets too convoluted in the accessor so I let the language do it, whether it's Ruby, Perl or Python. Where I put the filtering logic is based on how big the XML data set is and whether there are a lot of different uid values I'll want to grab. Sometimes letting the XPath engine do the heavy lifting makes sense, other times its easier to let XPath grab all the object nodes and filter in the calling language.
It seems with all the rich amount of function in xpath that you could do an "if" . However , my engine keeps insisting "there is no such function" , and I hardly find any documentation on the web (I found some dubious sources , but the syntax they had didn't work)
I need to remove ':' from the end of a string (if exist), so I wanted to do this:
if (fn:ends-with(//div [#id='head']/text(),': '))
then (fn:substring-before(//div [#id='head']/text(),': ') )
else (//div [#id='head']/text())
Any advice?
Yes, there is a way to do it in XPath 1.0:
concat(
substring($s1, 1, number($condition) * string-length($s1)),
substring($s2, 1, number(not($condition)) * string-length($s2))
)
This relies on the concatenation of two mutually exclusive strings, the first one being empty if the condition is false (0 * string-length(...)), the second one being empty if the condition is true. This is called "Becker's method", attributed to Oliver Becker (original link is now dead, the web archive has a copy).
In your case:
concat(
substring(
substring-before(//div[#id='head']/text(), ': '),
1,
number(
ends-with(//div[#id='head']/text(), ': ')
)
* string-length(substring-before(//div [#id='head']/text(), ': '))
),
substring(
//div[#id='head']/text(),
1,
number(not(
ends-with(//div[#id='head']/text(), ': ')
))
* string-length(//div[#id='head']/text())
)
)
Though I would try to get rid of all the "//" before.
Also, there is the possibility that //div[#id='head'] returns more than one node.
Just be aware of that — using //div[#id='head'][1] is more defensive.
The official language specification for XPath 2.0 on W3.org details that the language does indeed support if statements. See Section 3.8 Conditional Expressions, in particular. Along with the syntax format and explanation, it gives the following example:
if ($widget1/unit-cost < $widget2/unit-cost)
then $widget1
else $widget2
This would suggest that you shouldn't have brackets surrounding your expressions (otherwise the syntax looks correct). I'm not wholly confident, but it's surely worth a try. So you'll want to change your query to look like this:
if (fn:ends-with(//div [#id='head']/text(),': '))
then fn:substring-before(//div [#id='head']/text(),': ')
else //div [#id='head']/text()
I do strongly suspect this may fix it however, as the fact that your XPath engine seems to be trying to interpret if as a function, where it is in fact a special construct of the language.
Finally, to point out the obvious, insure that your XPath engine does in fact support XPath 2.0 (as opposed to an earlier version)! I don't believe conditional expressions are part of previous versions of XPath.
How about using fn:replace(string,pattern,replace) instead?
XPATH is very often used in XSLTs and if you are in that situation and does not have XPATH 2.0 you could use:
<xsl:choose>
<xsl:when test="condition1">
condition1-statements
</xsl:when>
<xsl:when test="condition2">
condition2-statements
</xsl:when>
<xsl:otherwise>
otherwise-statements
</xsl:otherwise>
</xsl:choose>
according to pkarat's, law you can achieve conditional XPath in version 1.0.
For your case, follow the concept:
concat(substring-before(your-xpath[contains(.,':')],':'),your-xpath[not(contains(.,':'))])
This will definitely work. See how it works. Give two inputs
praba:
karan
For 1st input: it contains : so condition true, string before : will be the output, say praba is your output. 2nd condition will be false so no problems.
For 2nd input: it does not contain : so condition fails, coming to 2nd condition the string doesn't contain : so condition true... therefore output karan will be thrown.
Finally your output would be praba,karan.
Personally, I would use XSLT to transform the XML and remove the trailing colons. For example, suppose I have this input:
<?xml version="1.0" encoding="UTF-8"?>
<Document>
<Paragraph>This paragraph ends in a period.</Paragraph>
<Paragraph>This one ends in a colon:</Paragraph>
<Paragraph>This one has a : in the middle.</Paragraph>
</Document>
If I wanted to strip out trailing colons in my paragraphs, I would use this XSLT:
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:fn="http://www.w3.org/2005/xpath-functions"
version="2.0">
<!-- identity -->
<xsl:template match="/|#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<!-- strip out colons at the end of paragraphs -->
<xsl:template match="Paragraph">
<xsl:choose>
<!-- if it ends with a : -->
<xsl:when test="fn:ends-with(.,':')">
<xsl:copy>
<!-- copy everything but the last character -->
<xsl:value-of select="substring(., 1, string-length(.)-1)"></xsl:value-of>
</xsl:copy>
</xsl:when>
<xsl:otherwise>
<xsl:copy>
<xsl:apply-templates/>
</xsl:copy>
</xsl:otherwise>
</xsl:choose>
</xsl:template>
</xsl:stylesheet>
Unfortunately the previous answers were no option for me so i researched for a while and found this solution:
http://blog.alessio.marchetti.name/post/2011/02/12/the-Oliver-Becker-s-XPath-method
I use it to output text if a certain Node exists. 4 is the length of the text foo. So i guess a more elegant solution would be the use of a variable.
substring('foo',number(not(normalize-space(/elements/the/element/)))*4)
Somewhat simpler XPath 1.0 solution, adapted from Tomalek's (posted here) and Dimitre's (here):
concat(substring($s1, 1 div number($cond)), substring($s2, 1 div number(not($cond))))
Note: I found an explicit number() was required to convert the bool to an int otherwise some XPath evaluators threw a type mismatch error. Depending on how strict your XPath processor is type-matching you may not need it.