Determining the Context Position

Similar to context size, context position, where you are in the node-set, is as important in determining what a style sheet needs at any one time. A typical example can be performing an action for every Nth node.

You can use the Sample XML Data File for XPath Context and Navigation, to display information for each day on a separate line, coloring the odd lines white and the even lines yellow. This provides easy legibility when there are a large amount of data to be displayed. Use the following XSLT template rule to display just the temperature values:

The following template rule display just the temperature values:

• The match pattern, match="weather/*", selects all children (*) of all children named "weather" of the context node, that is, of the document root node. Therefore, it selects a node-set consisting of the <today> element and the two <forecast> elements.
• The template rule declares a local variable, called odd_or_even, whose value is either the "odd" or "even" string, depending on the value of the position within the node-set of the node currently being processed.
• The test uses the position() function, which returns an integer whose value is that of the current node's position in the node-set. The test calculates the remainder of this integer when divided by 2. If the result is 0, then the result of the test is true, and $odd_or_even is "even"; otherwise it is "odd".
• The <xsl:choose> element that follows the variable's assignment tests the variable's value. If "odd", the temperature is inserted into a <p> element whose background-color is white; otherwise, the <p> element's background-color will be yellow.

Note   The use of the position() function in the <xsl:variable> code.

For more information about position(), see Processing Node-Sets by Using Node-Set Functions.

Example

XML File (weather.xml)

Change the href attribute in weather.xml (shown in Sample XML Data File for XPath Context and Navigation) to reference weathercontextposn.xsl.

XSLT File (weathercontextposn.xsl)

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

<xsl:template match="weather/*">
    <xsl:variable name="odd_or_even">
        <xsl:choose>
            <xsl:when test="position() mod 2 = 0">even</xsl:when>
            <xsl:otherwise>odd</xsl:otherwise>
        </xsl:choose>
    </xsl:variable>
    <xsl:choose>
        <xsl:when test="$odd_or_even = 'even'">
            <p style="background-color: yellow">even row: 
                <xsl:value-of select="./temperature" />
            </p>
        </xsl:when>
        <xsl:otherwise>
            <p style="background-color: white">odd row: 
                <xsl:value-of select="./temperature" />
            </p>
        </xsl:otherwise>
    </xsl:choose>
</xsl:template>

</xsl:stylesheet>

Formatted Output

Processor Output

<?xml version="1.0" encoding="UTF-16"?><p style="background-color: white">odd row: 
                76</p><p style="background-color: yellow">even row: 
                81</p><p style="background-color: white">odd row: 
                72</p>