Multiply 2 filtered numbers and sum - xslt

Question

I need to sum the multiplication of 2 numbers based on this example
<test>
<stop>
<id>1</id>
<unit_id>1</unit_id>
<unit_id>2</unit_id>
</stop>
<stop>
<id>2</id>
<unit_id>1</unit_id>
<unit_id>3</unit_id>
</stop>
<unit>
<id>1</id>
<count>2</count>
<value>1</value>
</unit>
<unit>
<id>2</id>
<count>4</count>
<value>1</value>
</unit>
<unit>
<id>3</id>
<count>2</count>
<value>3</value>
</unit>
The result i want to get is the one below
<test>
<stop>
<id>1</id>
<sum>6</sum>
</stop>
<stop>
<id>2</id>
<sum>10</sum>
</stop>
Any tips how to get it?
I tried with this example but the sum of the moltiplication doesn't work, it is ok for only the sum or the multiplication but not both
<xsl:template match="stop">
<xsl:variable name="ship_unit" select="id"/>
<xsl:value-of select="sum(following-sibling::unit[id=$ship_unit]/count*following-sibling::unit[id=$ship_unit]/value)"/>

Answer 1

If I am guessing correctly, you want to do something like:
XSLT 1.0
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="utf-8" indent="yes"/>
<xsl:key name="unit" match="unit" use="id" />
<xsl:template match="/test">
<xsl:copy>
<xsl:for-each select="stop">
<xsl:variable name="unit1" select="key('unit', unit_id[1])" />
<xsl:variable name="unit2" select="key('unit', unit_id[2])" />
<xsl:copy>
<xsl:copy-of select="id"/>
<sum>
<xsl:value-of select="$unit1/count * $unit1/value + $unit2/count * $unit2/value" />
</sum>
</xsl:copy>
</xsl:for-each>
</xsl:copy>
</xsl:template>
</xsl:stylesheet>
However, the result of applying this to your input example will be:
<?xml version="1.0" encoding="utf-8"?>
<test>
<stop>
<id>1</id>
<sum>6</sum>
</stop>
<stop>
<id>2</id>
<sum>8</sum>
</stop>
</test>
and not what you posted.