number()

Description

number() converts its argument to a number using XPath 1.0 numeric conversion rules:

• String: the string is stripped of leading and trailing whitespace and then parsed as a decimal number. If it cannot be parsed, the result is NaN.
• Boolean: true converts to 1, false converts to 0.
• Node-set: the node-set is first converted to its string value (same as calling string() on it), and then that string is converted to a number.
• Number: returned unchanged.

When called with no arguments, number() converts the string value of the context node.

number() is essential when you need to perform arithmetic on element content or attribute values that XPath does not automatically treat as numbers, or when you want to explicitly coerce a value and test for NaN before proceeding.

Parameters

Return value

xs:double — the numeric value, or NaN if conversion fails.

Examples

Arithmetic on element content

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<prices>
  <price>12.50</price>
  <price>7.99</price>
  <price>3.00</price>
</prices>

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/prices">
    <result>
      <total><xsl:value-of select="sum(price)"/></total>
      <first-doubled><xsl:value-of select="number(price[1]) * 2"/></first-doubled>
    </result>
  </xsl:template>
</xsl:stylesheet>

Output:

<result>
  <total>23.49</total>
  <first-doubled>25</first-doubled>
</result>

Guard against NaN before output

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<data>
  <value>42</value>
  <value>N/A</value>
</data>

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/data">
    <results>
      <xsl:for-each select="value">
        <xsl:variable name="n" select="number(.)"/>
        <item>
          <xsl:choose>
            <xsl:when test="$n = $n">
              <xsl:value-of select="$n"/>
            </xsl:when>
            <xsl:otherwise>invalid</xsl:otherwise>
          </xsl:choose>
        </item>
      </xsl:for-each>
    </results>
  </xsl:template>
</xsl:stylesheet>

Output:

<results>
  <item>42</item>
  <item>invalid</item>
</results>

Notes

• The XPath 1.0 idiom to detect NaN is $n != $n (or equivalently not($n = $n)), because NaN is the only value not equal to itself.
• Whitespace around numbers in element content is ignored: number(' 3.14 ') returns 3.14.
• Strings like "Infinity" and "-Infinity" are recognised by some processors as the numeric infinity values, but this is implementation-defined in XPath 1.0.
• In XSLT 2.0+, xs:double(), xs:integer(), and xs:decimal() provide schema-aware type casting and raise errors on invalid input instead of returning NaN.

See also

• floor()
• ceiling()
• round()
• format-number()