Proper use of for-each-group in XSLT - xslt

Question

I have the following xml sample:
<items>
<item>
<item_id>1</item_id>
<item_name>item 1</item_name>
<group_id>1</group_id>
<group_name>group 1</group_name>
</item>
<item>
<item_id>2</item_id>
<item_name>item 2</item_name>
<group_id>1</group_id>
<group_name>group 1</group_name>
</item>
<item>
<item_id>3</item_id>
<item_name>item 3</item_name>
<group_id>2</group_id>
<group_name>group 2</group_name>
</item>
</items>
which I need transformed into the following csv format:
1,item 1
2,item 2
3,item 3
1,group 1
2,group 2
In the xml, item_id will always be followed by item_name. The item name will not always be concat('item_',#). It could be an description such as 'toothpaste'. Items will never be repeated in the file but occasionally the group_id->group_name pairing will not always be 1-1. In this case, it is preferred to take the first pairing.
I am accomplishing this using a 'for-each-group' statement but it seems a bit hacky. Are there any downsides to this approach? What are some better ways to accomplish this?
<xsl:template match="/">
<xsl:call-template name="list_format">
<xsl:with-param name="list" select="'item'"/>
</xsl:call-template>
<xsl:call-template name="list_format">
<xsl:with-param name="list" select="'group'"/>
</xsl:call-template>
</xsl:template>
<xsl:template name="list_format">
<xsl:param name="list"/>
<xsl:variable name="linefeed" select="'
'"></xsl:variable>
<xsl:variable name="list_id" select="concat($list,'_id')"></xsl:variable>
<xsl:variable name="list_name" select="concat($list,'_name')"></xsl:variable>
<xsl:for-each-group select="/items/item" group-by="*[name()=$list_id]">
<xsl:sort select="*[name()=$list_id]"/>
<xsl:value-of select="*[name()=$list_id]"/>
<xsl:text>,</xsl:text>
<xsl:value-of select="*[name()=$list_name]"/>
<xsl:value-of select="$linefeed"/>
</xsl:for-each-group>
</xsl:template>

Answer 1

hmmm .. not really a downside but it doesn't work in XSLT 1.0 as it doesn't support for-each-group :-/
I don't think you would need XSLT 1.0 solution .. but still am posting my work :) Check this out!
<?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="/items">
<xsl:call-template name="items_grouping">
<xsl:with-param name="list" select="'item'"/>
</xsl:call-template>
<xsl:call-template name="items_grouping">
<xsl:with-param name="list" select="'group'"/>
</xsl:call-template>
</xsl:template>
<xsl:template name="items_grouping">
<xsl:param name="list"/>
<xsl:variable name="linefeed" select="'
'"></xsl:variable>
<xsl:variable name="list_id" select="concat($list,'_id')"></xsl:variable>
<xsl:variable name="list_name" select="concat($list,'_name')"></xsl:variable>
<xsl:for-each select="item">
<xsl:for-each select="*[name()=$list_id and not(.= ../preceding-sibling::item/*[name()=$list_id]/.)]">
<xsl:value-of select="concat(.,',')"/>
<xsl:value-of select="../*[name()=$list_name]"/>
<xsl:value-of select="$linefeed"/>
</xsl:for-each>
</xsl:for-each>
</xsl:template>
<xsl:template match="text()"/>
</xsl:stylesheet>
Used same methodology of yours .. only change is 'preceding-sibling'
and also for this code, order of child-nodes of <item> doesn't matter

Answer 2

Here is a simple and short XSLT 2.0 (as requested) solution:
<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:strip-space elements="*"/>
<xsl:template match="/">
<xsl:apply-templates/>
<xsl:for-each-group select="/*/*/group_id" group-by=".">
<xsl:value-of separator="," select="../*[starts-with(name(), 'group_')]"/>
<xsl:text>
</xsl:text>
</xsl:for-each-group>
</xsl:template>
<xsl:template match="item">
<xsl:value-of separator="," select="*[starts-with(name(), 'item_')]"/>
<xsl:text>
</xsl:text>
</xsl:template>
</xsl:stylesheet>
when this transformation is applied on the provided XML document:
<items>
<item>
<item_id>1</item_id>
<item_name>item 1</item_name>
<group_id>1</group_id>
<group_name>group 1</group_name>
</item>
<item>
<item_id>2</item_id>
<item_name>item 2</item_name>
<group_id>1</group_id>
<group_name>group 1</group_name>
</item>
<item>
<item_id>3</item_id>
<item_name>item 3</item_name>
<group_id>2</group_id>
<group_name>group 2</group_name>
</item>
</items>
the wanted, correct result is produced:
1,item 1
2,item 2
3,item 3
1,group 1
2,group 2