sum()

Description

sum() converts each node in a node-set to a number (using the XPath number() rules) and returns their total as a double. If any node cannot be converted to a number, its value is treated as NaN, and the entire result is NaN.

In XSLT 2.0+, sum() accepts any sequence of atomic values that can be added together. A second argument may be provided as a zero value to return when the sequence is empty (in XPath 1.0, sum() on an empty node-set returns 0).

sum() is the standard way to compute totals over repeated elements, such as order amounts, quantities, or scores, without writing an explicit loop.

Parameters

Return value

xs:double (XPath 1.0) or the type matching the input sequence (XPath 2.0+) — the numeric sum of all items.

Examples

Sum all child element values

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<invoice>
  <line amount="29.99"/>
  <line amount="14.50"/>
  <line amount="5.00"/>
</invoice>

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="text"/>

  <xsl:template match="/invoice">
    <xsl:text>Total: </xsl:text>
    <xsl:value-of select="sum(line/@amount)"/>
  </xsl:template>
</xsl:stylesheet>

Output:

Total: 49.49

Conditional sum (sum filtered values)

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<sales>
  <sale region="North" amount="100"/>
  <sale region="South" amount="250"/>
  <sale region="North" amount="175"/>
  <sale region="South" amount="80"/>
</sales>

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="/sales">
    <totals>
      <north><xsl:value-of select="sum(sale[@region='North']/@amount)"/></north>
      <south><xsl:value-of select="sum(sale[@region='South']/@amount)"/></south>
    </totals>
  </xsl:template>
</xsl:stylesheet>

Output:

<totals>
  <north>275</north>
  <south>330</south>
</totals>

Empty sequence with fallback (XSLT 2.0)

<!-- Returns 0 when there are no discount elements -->
<xsl:value-of select="sum(discount/@value, 0)"/>

Notes

• Nodes that cannot be converted to a number (e.g., text like "N/A") produce NaN, which propagates through the sum. Validate data or use number() with a fallback before summing.
• sum() on an empty node-set returns 0 in XPath 1.0. In XPath 2.0+, the second argument controls this behaviour.
• For an average, there is no built-in avg() in XPath 1.0. Compute it as sum(nodes) div count(nodes). XPath 2.0+ provides avg().
• sum() works on attribute nodes as well as element text nodes; the path sum(items/item/@qty) is valid.

See also

• count()