XPath Arithmetic Operators
In addition to selecting elements by location paths, XPath also provides capability for data manipulation. The numerical parts of an XML document can be added, divided, subtracted, and multiplied. Likewise, strings can be compared for equality.
XPath provides arithmetic operators for use within XPath
expressions. This capability comes in very handy in XSL transformations
that involve totaling an item list or applying discounts to product
prices for display in HTML. The operators available in XPath are
+, -, *,
div, and mod (addition, subtraction, multiplication,
division, and modulus, respectively.) There are also functions such as
sum that allow you to total sets of
numbers and perform other tasks. We cover functions in the next
section.
Imagine that you have an XML file containing a list of products, and you want to display these products in another application (such as your web site) but need to apply a 20% discount to all retail prices. You can use the XPath arithmetic operators to solve this problem. Let’s turn to the source XML document (products.xml) shown in Example 5-3.
<?xml version="1.0" encoding="UTF-8"?>
<products>
<item name="bowl" price="19.95"/>
<item name="spatula" price="4.95"/>
<item name="power mixer" price="149.95"/>
<item name="chef hat" price="39.95"/>
</products>To apply a blanket 20% discount to all products, you can use XPath
from within an XSLT document. The XSLT shown in Example 5-4 (products.xsl ) does the trick.
<?xml version="1.0" encoding="iso-8859-1"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
<html>
<body>
<xsl:apply-templates/>
</body>
</html>
</xsl:template>
<xsl:template match="item">
<p><b>Item:</b> <xsl:value-of select="@name"/>
Orig. Price: <xsl:value-of select="@price"/>, Our Price:
<xsl:value-of select="@price * 0.8"/>
</p>
</xsl:template>
</xsl:stylesheet>The XPath numerical expressions are in the xsl:value-of elements. The discount is
achieved by multiplying the value of the price attribute by 0.8. You can run the transformation using the
4xslt tool illustrated in the
previous chapter:
$ 4xslt.bat products.xml products.xsl
<html>
<body>
<p>
<b>Item: </b>bowl
Orig. Price: 19.95, Our Price: 15.96</p>
<p>
<b>Item: </b>spatula
Orig. Price: 4.95, Our Price: 3.96</p>
<p>
<b>Item: </b>power mixer
Orig. Price: 149.95, Our Price: 119.96</p>
<p>
<b>Item: </b>chef hat
Orig. Price: 39.95, Our Price: 31.96</p>
</body>
</html>The div and mod operators work as the others do. For
example, @price div 2 divides all
prices designated by 2.