Using XSLT to Group Data Based on Substrings

I am trying to use XSLT to group data from an XML document into two categories. Specifically, given a list of three items, I want the XSLT to export the three items as two different groups (food & buildings). I'm attempting to do this by grouping the data by substrings.

XML:

<?xml version="1.0" encoding="UTF-8"?>
<items> 
    <Skyscraper>Willis Tower</Skyscraper> 
    <Small_fruit>blueberry</Small_fruit> 
    <Big_fruit>watermelon </Big_fruit> 
</items>

What I tried (XSLT):

<?xml version="1.1" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:xs="http://www.w3.org/2001/XMLSchema" exclude-result-prefixes="xs" version="2.0">
    <xsl:output method="xml"/>  
    <xsl:template match = "/">      
        <items>
            <xsl:element name = "Fruit">
                <xsl:for-each-group select="//items" group-by="*[contains(local-name(), 'fruit')]">
                    <xsl:copy-of select = "."/>
                    <xsl:value-of select="current-grouping-key()"/>
                    <xsl:if test = "not(position() = last())">,</xsl:if>
                </xsl:for-each-group>
            </xsl:element>
        </items>
    </xsl:template> 
</xsl:stylesheet>

What I expected (XML):

<?xml version="1.0" encoding="UTF-8"?>
<items> 
    <Building>
        <Skyscraper>Willis Tower</Skyscraper>
    </Building> 
    <Food>
        <Small_fruit>blueberry</Small_fruit> 
        <Big_fruit>watermelon </Big_fruit> 
    </Food>
</items>

Edited XSLT

<?xml version="1.1" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:xs="http://www.w3.org/2001/XMLSchema" exclude-result-prefixes="xs" version="2.0">
    <!-- airport XSLT -->
    <xsl:output method="xml"/>  
    <xsl:template match = "/">      
        <items>
            <xsl:element name = "fruit">
                <xsl:for-each-group select="/items/*" group-by="*[contains(local-name(), 'fruit')]">
                    <xsl:copy-of select = "."/>
                    <xsl:value-of select="current-grouping-key()"/>
                    <xsl:if test = "not(position() = last())">&#xa;</xsl:if>
                </xsl:for-each-group>
            </xsl:element>
            <xsl:element name = "building">
                <xsl:for-each-group select="/items/*" group-by="*[contains(local-name(), 'sky')]">
                    <xsl:copy-of select = "."/>
                    <xsl:value-of select="current-grouping-key()"/>
                    <xsl:if test = "not(position() = last())">&#xa;</xsl:if>
                </xsl:for-each-group>
            </xsl:element>
        </items>
    </xsl:template> 
</xsl:stylesheet>

Try it this way?

XSLT 2.0

<xsl:stylesheet version="2.0" 
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>

<xsl:template match="/items">      
    <items>
        <xsl:for-each-group select="*" group-by="contains(local-name(), 'fruit')">
            <xsl:element name="{if(current-grouping-key()) then 'Food' else 'Building'}">
                <xsl:copy-of select="current-group()"/>
            </xsl:element>
        </xsl:for-each-group>
    </items>
</xsl:template>

</xsl:stylesheet>

P.S. You could also do simply:

<xsl:stylesheet version="2.0" 
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>

<xsl:template match="/items">   
    <xsl:variable name="fruit" select="*[contains(local-name(), 'fruit')]" />   
    <items>
        <Building>
            <xsl:copy-of select="* except $fruit"/>
        </Building>
        <Food>
            <xsl:copy-of select="$fruit"/>
        </Food>
    </items>
</xsl:template>

</xsl:stylesheet>

The difference is this will always create both groups, even if one (or both) of them is empty.