xml - XSLT for-each-group group-by variable -

i trying achieve more flexible groub-by statement xslt, using variable (depending of variable value, there different grouping needed):

.......     <xsl:param name="rows"/>     <xsl:variable name="groupby">         <xsl:choose>             <xsl:when test="$report_type='first_type'">                 <xsl:value-of select="concat(date,ccy)"/>             </xsl:when>             <xsl:otherwise>                 <xsl:value-of select="concat(type,ccy)"/>             </xsl:otherwise>         </xsl:choose>     </xsl:variable>     <xsl:for-each-group select="$rows" group-by="$groupby">     .....     </xsl:for-each-group> 

as far know kind of construction won't work (well, didn't work me).

my question is: how pass variable group-by attribute?

thank in advance kind of help.

the problem here not "how pass variable group-by attribute", content of passed variable. group-by attribute must contain xpath expression - passing string value.

if there 2 ways group nodes, suggest use following construct:

<xsl:for-each-group select="item" group-by="if($report_type='first_type') concat(date,ccy) else concat(type,ccy)">