Flatten nodes that have repeated child node using XSLT - xslt-1.0

Question

I have a document of following structure (this is just an example to help me verbalize the problem), that I'm trying to flatten. By flattening I mean copying all the <Report_Entry> nodes with several <Event>s so that each <Report_Entry> node contained just a single <Event>
What I have:
<?xml version="1.0"?>
<Report_Data>
<Report_Entry>
<ID>1</ID>
<Event>
<Start_Date>2011-09-06</Start_Date>
<End_Date>2011-09-10</End_Date>
</Event>
<Event>
<Start_Date>2011-09-10</Start_Date>
<End_Date>2011-09-15</End_Date>
</Event>
<Event>
<Start_Date>2011-09-15</Start_Date>
<End_Date>2011-09-20</End_Date>
</Event>
</Report_Entry>
<Report_Entry>
<ID>2</ID>
<Event>
<Start_Date>2011-09-20</Start_Date>
<End_Date>2011-09-25</End_Date>
</Event>
<Event>
<Start_Date>2011-09-25</Start_Date>
<End_Date>2011-09-30</End_Date>
</Event>
</Report_Entry>
<Report_Entry>
<ID>3</ID>
<Event>
<Start_Date>2011-09-30</Start_Date>
<End_Date>2011-10-05</End_Date>
</Event>
</Report_Entry>
</Report_Data>
What I'm trying to get:
<?xml version="1.0"?>
<Report_Data>
<Report_Entry>
<ID>1</ID>
<Event>
<Start_Date>2011-09-06</Start_Date>
<End_Date>2011-09-10</End_Date>
</Event>
</Report_Entry>
<Report_Entry>
<ID>1</ID>
<Event>
<Start_Date>2011-09-10</Start_Date>
<End_Date>2011-09-15</End_Date>
</Event>
</Report_Entry>
<Report_Entry>
<ID>1</ID>
<Event>
<Start_Date>2011-09-15</Start_Date>
<End_Date>2011-09-20</End_Date>
</Event>
</Report_Entry>
<Report_Entry>
<ID>2</ID>
<Event>
<Start_Date>2011-09-20</Start_Date>
<End_Date>2011-09-25</End_Date>
</Event>
</Report_Entry>
<Report_Entry>
<ID>2</ID>
<Event>
<Start_Date>2011-09-25</Start_Date>
<End_Date>2011-09-30</End_Date>
</Event>
</Report_Entry>
<Report_Entry>
<ID>3</ID>
<Event>
<Start_Date>2011-09-30</Start_Date>
<End_Date>2011-10-05</End_Date>
</Event>
</Report_Entry>
</Report_Data>
Here is XSLT that I'm using:
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="node() | #*">
<xsl:copy>
<xsl:apply-templates select="node() | #*"/>
</xsl:copy>
</xsl:template>
<xsl:template match="Report_Entry">
<xsl:for-each select="Event">
<Report_Entry>
<xsl:copy-of select="../*[not(self::Event)]"/>
<xsl:copy-of select="."/>
</Report_Entry>
</xsl:for-each>
</xsl:template>
</xsl:stylesheet>
It works, though I feel that there might be a better, faster and more universal solution. In particular, I don't like "hardcoding" <Report_Entry> since this way I wouldn't be able to copy its attributes (if any). Are there other ways/templates to deal with this problem?

Answer 1

As simple as this:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:strip-space elements="*"/>
<xsl:template match="/*">
<Report_Data>
<xsl:apply-templates select="*/Event"/>
</Report_Data>
</xsl:template>
<xsl:template match="Event">
<Report_Entry>
<xsl:copy-of select="../ID | ."/>
</Report_Entry>
</xsl:template>
</xsl:stylesheet>
When this transformation is applied on the provided XML document:
<Report_Data>
<Report_Entry>
<ID>1</ID>
<Event>
<Start_Date>2011-09-06</Start_Date>
<End_Date>2011-09-10</End_Date>
</Event>
<Event>
<Start_Date>2011-09-10</Start_Date>
<End_Date>2011-09-15</End_Date>
</Event>
<Event>
<Start_Date>2011-09-15</Start_Date>
<End_Date>2011-09-20</End_Date>
</Event>
</Report_Entry>
<Report_Entry>
<ID>2</ID>
<Event>
<Start_Date>2011-09-20</Start_Date>
<End_Date>2011-09-25</End_Date>
</Event>
<Event>
<Start_Date>2011-09-25</Start_Date>
<End_Date>2011-09-30</End_Date>
</Event>
</Report_Entry>
<Report_Entry>
<ID>3</ID>
<Event>
<Start_Date>2011-09-30</Start_Date>
<End_Date>2011-10-05</End_Date>
</Event>
</Report_Entry>
</Report_Data>
the wanted, correct result is produced:
<Report_Data>
<Report_Entry>
<ID>1</ID>
<Event>
<Start_Date>2011-09-06</Start_Date>
<End_Date>2011-09-10</End_Date>
</Event>
</Report_Entry>
<Report_Entry>
<ID>1</ID>
<Event>
<Start_Date>2011-09-10</Start_Date>
<End_Date>2011-09-15</End_Date>
</Event>
</Report_Entry>
<Report_Entry>
<ID>1</ID>
<Event>
<Start_Date>2011-09-15</Start_Date>
<End_Date>2011-09-20</End_Date>
</Event>
</Report_Entry>
<Report_Entry>
<ID>2</ID>
<Event>
<Start_Date>2011-09-20</Start_Date>
<End_Date>2011-09-25</End_Date>
</Event>
</Report_Entry>
<Report_Entry>
<ID>2</ID>
<Event>
<Start_Date>2011-09-25</Start_Date>
<End_Date>2011-09-30</End_Date>
</Event>
</Report_Entry>
<Report_Entry>
<ID>3</ID>
<Event>
<Start_Date>2011-09-30</Start_Date>
<End_Date>2011-10-05</End_Date>
</Event>
</Report_Entry>
</Report_Data>

Answer 2

Your answer couldn't be much simpler, so no need to worry on that front. When writing code, but especially XSLT, the clarity of the code tends to be worth a lot more than its ultimate efficiency.
As for the hardcoded element name and copying attributes, here's a start:
<xsl:template match="Report_Entry">
<xsl:variable name="parent-name" select="name()"/>
<xsl:variable name="parent-attributes" select="#*"/>
<xsl:for-each select="Event">
<xsl:element name="{$parent-name}">
<xsl:copy-of select="$parent-attributes"/>
<xsl:copy-of select="../*[not(self::Event)]"/>
<xsl:copy-of select="."/>
</xsl:element>
</xsl:for-each>
</xsl:template>
variables are used to stash some of the context as it exists outside the for-each. element makes an element that's a look-alike for your original, no matter what it's called, and the first copy-of makes it more convincing by copying in the original's attributes as well. Now, if your data suddenly takes on attributes, you'll be ready.
The non-hardcodedness of the name doesn't mean much in this case, but it would if, say, you were to factor out that part to a separate template and call it from multiple places:
<xsl:template name="collapse-the-thing">
<xsl:param name="context"/>
<xsl:param name="sub-element-name" select="'Event'"/>
<xsl:variable name="parent-name" select="name($context)"/>
<xsl:variable name="parent-attributes" select="$context/#*"/>
<xsl:for-each select="$context/*[name()=$sub-element-name]">
<xsl:element name="{$parent-name}">
<xsl:copy-of select="$parent-attributes"/>
<xsl:copy-of select="../*[name()!=$sub-element-name]"/>
<xsl:copy-of select="."/>
</xsl:element>
</xsl:for-each>
</xsl:template>
<xsl:template match="Report_Entry">
<xsl:call-template name="collapse-the-thing">
<xsl:with-param name="context" select="."/>
</xsl:call-template>
</xsl:template>
<xsl:template match="Some_Other_Entry">
<xsl:call-template name="collapse-the-thing">
<xsl:with-param name="context" select="."/>
<xsl:param name="sub-element-name" select="'Happening'"/>
</xsl:call-template>
</xsl:template>
Hope that was enlightening. Enjoy!