XSL joining 2 group statements for output - xslt

Question

using saxon, i'm trying to print the totals from a table fetched by sql printed to a csv in a specific format.
the structure should be something like, and the totals i'm trying to get can be seen here too:
to keep in mind col2 can have any letter, but col4 can have only a, b or c
rough idea of how the input looks:
<ROW>
<ROW[1]>
<col1>1</col1>
<col2>a</col2>
<col3>1</col3>
<col4>a</col4>
</ROW[1]>
<ROW[2]>
<col1>2</col1>
<col2>a</col2>
<col3>2</col3>
<col4>a</col4>
</ROW[2]>
<ROW[3]>
<col1>3</col1>
<col2>a</col2>
<col3>3</col3>
<col4>a</col4>
</ROW[3]>
<ROW[4]>
<col1>6</col1>
<col2>b</col2>
<col3>2</col3>
<col4>a</col4>
</ROW[4]>
...
</ ROW>
doing totals just for col1 should be easy enough:
<xsl:template name = "totals">
<xsl:for-each-group select = "//ROW" group-by="col2">
<xsl:variable name="group_total">
<xsl:value-of select="sum(current-group()/col1)"/>
<xsl:value-of select="';'"/>
</xsl:variable>
<xsl:value-of select="'
'"/>
</xsl:for-each-group>
</xsl:template>
but what would be the best way to join totals for col3 in the same row, like totals for a are next to a?
i thought calling a template and passing col2 value to run the totals by the same principle, but that has a problem when col2 doesn't have a value from col4

Answer 1

I am not good at imagining input structures but if you declare a key <xsl:key name="by-col4" match="ROW" use="col4"/> and then use sum(key('by-col4', current-grouping-key())/col3) inside of your for-each-group it might give the result you have shown.