Comparisons

To compare two objects in XPath, use the = sign to test for equality, or use != to test for inequality.

For a comparison operation, exactly two operands must be supplied. Comparisons are then made by evaluating each operand, and converting them as needed, so they are of the same type. This is done according to the process described below, in Order of Precedence For Comparsions.

All elements and attributes are strings, but are automatically cast as integer values for numeric comparisons. Literal numeric values are cast to long or double types during comparison operations, as shown in the following table.

For information about < and other binary comparison operators, see Binary Comparison Operators, below.

Single or double quotation marks can be used for string delimiters in expressions. This makes it easier to construct and pass patterns from within scripting languages.

For more information about how comparisons are performed using XPath, see section 3.4 ("Booleans") of the W3C XML Path Language (XPath) Recommendation.

Examples

Order of Precedence for Comparisons

Comparisons with regard to data types obey the order of precedence.

• If at least one operand is a Boolean, each operand is first converted to a Boolean.
• Otherwise, if at least one operand is a number, each operand is first converted to a number.
• Otherwise, if at least one operand is a date, each operand is first converted to a date.
• Otherwise, both operands are first converted to strings.

Binary Comparison Operators

A set of binary comparison operators compares numbers and strings and returns Boolean results. The <, <=, >, and >= operators are used for less than, less than or equal, greater than, and greater than or equal, respectively. Single or double quotation marks can be used for string delimiters in expressions. This makes it easier to construct and pass patterns within scripting languages.

Examples

Example

XML File (test.xml)

<?xml version="1.0"?>
<test>

    <x a="1">
      <x a="2" b="B">
        <x>
          <y>y31</y>
          <y>y32</y>
        </x>
      </x>
    </x>

    <x a="2">
      <y>y2</y>
    </x>

    <x a="3">
      <y>y3</y>
    </x>

</test>

XSLT File (test.xsl)

The following XSLT style sheet selects all the <x> elements that are the first of their siblings in the document order.

<?xml version='1.0'?>
<xsl:stylesheet version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:output method="xml" omit-xml-declaration="yes" indent="yes"/>

<!-- Suppress text nodes not covered in subsequent template rule. -->
<xsl:template match="text()"/>

<xsl:template match="*">
   <xsl:element name="{name()}">
      <xsl:apply-templates select="*|@*"/>
      <xsl:if test="text()">
         <xsl:value-of select="."/>
      </xsl:if>
   </xsl:element>
</xsl:template>

<xsl:template match="@*">
   <xsl:attribute name="{name()}">
      <xsl:value-of select="."/>
   </xsl:attribute>
</xsl:template>

<xsl:template match="/test">
  <xsl:apply-templates select="//x[position() = 1 ] "/>
</xsl:template>

</xsl:stylesheet>

Formatted Output

The transformation applied to the XML file above yields the following result:

<x a="1">
  <x a="2" b="B">
     <x>
        <y>y31</y>
        <y>y32</y>
     </x>
   </x>
</x>
<x a="2" b="B">
   <x>
      <y>y31</y>
      <y>y32</y>
   </x>
</x>
<x>
   <y>y31</y>
   <y>y32</y>
</x>

See Also

Sample XML File for XPath Syntax (inventory.xml) | XPath Examples