Finding unique nodes with xslt inside a for-each - xslt

Question

Source XML:
<r:root xmlns:r="http://root/">
<p:parent xmlns:p="http://parent/">
<p:name>John</name>
<p:age>30</age>
<c:child xmlns:c="http://child/">
<c:cname>John_child_1</cname>
<c:cage/>
<c:ItemNumber>1</ItemNumber>
</child>
<c:child xmlns:c="http://child/">
<c:cname>John_child_2</cname>
<c:cage/>
<c:ItemNumber>2</ItemNumber>
</child>
<c:child xmlns:c="http://child/">
<c:cname>John_child_3</cname>
<c:cage/>
<c:ItemNumber>1</ItemNumber>
</child>
</parent>
<p:parent>
<p:name>Doe</name>
<p:age>40</age>
<c:child xmlns:c="http://child/">
<c:cname>Doe_child_1</cname>
<c:cage/>
<c:ItemNumber>2</ItemNumber>
</child>
<c:child xmlns:c="http://child/">
<c:cname>Doe_child_2</cname>
<c:cage/>
<c:ItemNumber>2</ItemNumber>
</child>
</parent>
...
...
...
Target XML:
<root>
<f:father xmlns:f="http://father/">
<f:name>John</name>
<f:age>30</age>
<f:UniqueItemNumber>1</UniqueItemNumber>
<c:child xmlns:c="http://child/">
<c:cname>John_child_1</cname>
<c:cage/>
<c:ItemNumber>1</ItemNumber>
</child>
<c:child xmlns:c="http://child/">
<c:cname>John_child_3</cname>
<c:cage/>
<c:ItemNumber>1</ItemNumber>
</child>
</father>
<f:father xmlns:f="http://father/">
<f:name>John</name>
<f:age>30</age>
<f:UniqueItemNumber>2</UniqueItemNumber>
<c:child xmlns:c="http://child/">
<c:cname>John_child_2</cname>
<c:cage/>
<c:ItemNumber>2</ItemNumber>
</child>
</father>
<f:father xmlns:f="http://father/">
<f:name>Doe</name>
<f:age>40</age>
<f:UniqueItemNumber>2</UniqueItemNumber>
<c:child xmlns:c="http://child/">
<c:cname>Doe_child_1</cname>
<c:cage/>
<c:ItemNumber>2</ItemNumber>
</child>
<c:child xmlns:c="http://child/">
<c:cname>Doe_child_2</cname>
<c:cage/>
<c:ItemNumber>2</ItemNumber>
</child>
</father>
....
...
I have a source xml, which I want to convert to the shown Target xml using XSLT.
In source, we can have more than 1 parent elements, each containing multiple child. To generate the target, first we should find the distinct list of ItemNumber of all childs for each parent. Hence, the Father element in the target xml should be mapped for each unique ItemNumber in the source xml. You can say that it's like group-by clause of sql, where we are grouping on ItemNumber for each Parent. I hope that the example explains the situation.
I have been trying all sorts of thing but haven't reached even near to the solution. I am running into multiple issues while forming a solution:
1. I don't think that I can apply "Muenchian Method" since, I need to find unique ItemNumber for each Parent. Hence, the key has to be defined inside the for-each(parent) element. I am confused here.
2. I think, I should be having a top level for-each(Parent). Inside it, a way to determine unique ItemNumber. And then, when I try to use to get Parent Name, I get nothing because the xpath (/name) isn;t valid when the control is inside the second for-each(uniqueItemNumber). It's tough to explain the problem.
I am hoping that I can get a solution here. Thanks in advance.

Answer 1

You can use Muenchian grouping to group within an element like this, the trick is to include something unique to each parent element as part of the grouping key. Its generate-id() is usually a good candidate.
<xsl:key name="childrenByNumber "match="c:child"
use="concat(generate-id(..), '+', c:ItemNumber)"/>
When you want to extract the groups within a parent you construct the lookup key in the same way:
<xsl:template match="p:parent">
<xsl:variable name="p" select="."/>
<xsl:for-each select="c:child[generate-id() =
generate-id(key('childrenByNumber', concat(generate-id($p), '+', c:ItemNumber))[1])]">
<f:father xmlns:f="http://father/">
<f:name><xsl:value-of select="$p/p:name"/></f:name>
<f:age><xsl:value-of select="$p/p:age"/></f:age>
<f:uniqueItemNumber>
<xsl:value-of select="c:ItemNumber"/>
</f:uniqueItemNumber>
<xsl:copy-of select="key('childrenByNumber', concat(generate-id($p), '+', c:ItemNumber))"/>
</f:father>
</xsl:for-each>
</xsl:template>