Xslt copy element to existing or create new if not exists - xslt

Question

Pretty new to xml transformations and i'm stuck at (might be for you) pretty easy task.
Let's suggest we have source:
<root>
<someValue>123</someValue>
</root>
It should be transformed into:
<root>
<additional>
<someValue>123</someValue>
</additional>
</root>
But if we have this as a source:
<root>
<additional>
<b>something</b>
</additional>
<someValue>123</someValue>
</root>
we should move someValue to existing additional, i.e.:
<root>
<additional>
<b>something</b>
<someValue>123</someValue>
</additional>
</root>
Keep in mind that there can be other elements at a level with same behavior (moved under additional).
Well, working example is much appreciated, but if it is accompanied by small description of how it works that would be fantastic (i prefer be tought to fish, rather than just being fed with it).

Answer 1

One possible approach would be to add a additional wrapper as a child of root, and remove the existing additional wrapper - so its children move up to become children of root (or rather children of the added additional wrapper):
XSLT 1.0
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:strip-space elements="*"/>
<!-- identity transform -->
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="/root">
<xsl:copy>
<additional>
<xsl:apply-templates/>
</additional>
</xsl:copy>
</xsl:template>
<xsl:template match="additional">
<xsl:apply-templates/>
</xsl:template>
</xsl:stylesheet>

Answer 2

Keep in mind that there can be other elements at a level with same
behavior (moved under additional).
This stylesheet:
<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="root[additional|someValue]">
<xsl:copy>
<xsl:apply-templates select="#*"/>
<additional>
<xsl:apply-templates select="additional/*|someValue"/>
</additional>
<xsl:apply-templates select="node()[not(self::additional|self::someValue)]"/>
</xsl:copy>
</xsl:template>
</xsl:stylesheet>
With this input:
<root>
<additional>
<b>something</b>
</additional>
<someValue>123</someValue>
<anotherValue>keep</anotherValue>
</root>
Output:
<root>
<additional>
<b>something</b>
<someValue>123</someValue>
</additional>
<anotherValue>keep</anotherValue>
</root>
Do note: just one rule to override the identity transformation. Only process root meeting the conditions (someValue or additional childs). Copying root, applying templates to attributes (to further process), wrapping with an additional element the result of applying templates to additional's childs and root's someValue childs. Finally, applying templates to root's childs, which are not additional nor someValue.

Answer 3

I ended up with following:
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:strip-space elements="*"/>
<!-- identity transform -->
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="/root/additional"/>
<xsl:template match="/root">
<xsl:copy>
<additional>
<xsl:copy-of select="someValue"/>
<xsl:copy-of select="additional/*"/>
</additional>
</xsl:copy>
</xsl:template>
Here we strip original additional and then create it from scratch copying there needed someValue and original content from source (additional/*)

Answer 4

Use for version xslt 2.0
<?xml version="1.0" 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" omit-xml-declaration="no" indent="yes"/>
<xsl:strip-space elements="*"/>
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node() except someValue"/>
</xsl:copy>
</xsl:template>
<xsl:template match="additional">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
<xsl:copy-of select="following-sibling::someValue"/>
</xsl:copy>
</xsl:template>
</xsl:stylesheet>