Move child Nodes to attributes conditionally

Question

I am trying to transform this document but am fairly new to xslt and having tons of fun trying to get it right. The core node(truncated for simplicity) looks like this

<Product prod_id="6352">
    <brandId>221</brandId>
    <brand>Oscar Mayer</brand>
    <images>
       <smallimage>text</simage>
       <medimage>text</medimage>
       <largeimage>text</limage>
    </images>
    <nutrition>
        <nutritionShow>Y</nutritionShow>
        <servingSize>1 SLICE</servingSize>
        <servingsPerContainer>12</servingsPerContainer>
        <totalCalories>60</totalCalories>
        <fatCalories>35</fatCalories>
        <totalFat>4</totalFat>
        <totalFatPercent>6</totalFatPercent>
        <totalFatUnit>g</totalFatUnit>
        <saturatedFat>1.5</saturatedFat>
        <saturatedFatPercent>8</saturatedFatPercent>
        <saturatedFatUnit>g</saturatedFatUnit>
        <transFat>0</transFat>
        <transFatUnit>g</transFatUnit>
        <cholesterolUnit>mg</cholesterolUnit>
    </nutrition>
    <prodId>6352</prodId>
</Product>

In the end I want to sub-nodes that are grouped logically to be a single node with appropriate attribute names.

The end result should look like this

<Product prod_id="6352">
<brandId>221</brandId>
<brand>Oscar Mayer</brand>
<images>
   <smallimage>text</smallimage>
   <medimage>text</medimage>
   <largeimage>text</largeimage>
</images>
<nutrition>
    <nutritionShow>Y</nutritionShow>
    <servingSize>1 SLICE</servingSize>
    <servingsPerContainer>12</servingsPerContainer>
    <totalCalories>60</totalCalories>
    <fatCalories>35</fatCalories>
    <totalFat amount="4" percent="6" unit="g" />
    <saturatedFat amount="1.5" percent="8" unit="g"/>
    <transFat amount="0" unit="g"</>
</nutrition>
<prodId>6352</prodId>

Some key features are

1. group the similar attributes(notice saturatedFat and transFat ... slightly different)I have a discrete list of these sets. You could use a list or something more dynamic based on relationships but notice the variance.
2. leave other(non group-able) attributes be
3. ignore groups that lack the amount attribute/only have unit attribute(notice cholesterol)

Thanks in advance for helping me to understand this fairly complex transformation.

Answer 1

One possible solution is following XSLT:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="html" encoding="UTF-8" indent="yes" />
 <xsl:strip-space elements="*"/>
  <xsl:template match="@*|node()">
    <xsl:copy>
      <xsl:apply-templates select="@*|node()"/>
    </xsl:copy>
  </xsl:template>
  <xsl:template match="nutrition/*">
    <xsl:variable name="cName" select="name()"/>
    <xsl:choose>
      <xsl:when test="following-sibling::node()[name()=concat($cName,'Unit')]">
        <xsl:copy>
          <xsl:attribute name="amount">
            <xsl:value-of select="."/>
          </xsl:attribute>
          <xsl:if test="following-sibling::node()[name()=concat($cName,'Percent')]">
            <xsl:attribute name="percent">
              <xsl:value-of select="following-sibling::node()[name()=concat($cName,'Percent')]"/>
            </xsl:attribute>
          </xsl:if>
          <xsl:attribute name="unit">
            <xsl:value-of select="following-sibling::node()[name()=concat($cName,'Unit')]"/>
          </xsl:attribute> 
        </xsl:copy>
      </xsl:when>
      <xsl:when test="contains(name() ,'Unit') or contains(name() ,'Percent')"/>
      <xsl:otherwise>
        <xsl:copy>
          <xsl:apply-templates />
        </xsl:copy>
      </xsl:otherwise>
    </xsl:choose>
  </xsl:template>
</xsl:stylesheet>

when applied to your input XML produces the ouput

<Product prod_id="6352">
  <brandId>221</brandId>
  <brand>Oscar Mayer</brand>
  <images>
    <smallimage>text</smallimage>
    <medimage>text</medimage>
    <largeimage>text</largeimage>
  </images>
  <nutrition>
    <nutritionShow>Y</nutritionShow>
    <servingSize>1 SLICE</servingSize>
    <servingsPerContainer>12</servingsPerContainer>
    <totalCalories>60</totalCalories>
    <fatCalories>35</fatCalories>
    <totalFat amount="4" percent="6" unit="g"></totalFat>
    <saturatedFat amount="1.5" percent="8" unit="g"></saturatedFat>
    <transFat amount="0" unit="g"></transFat>
  </nutrition>
  <prodId>6352</prodId>
</Product>

The first template is an Identity transform and copies all nodes and attributes without any changes.
The second temmplate matches all child elements/nodes of nutrition.
In case the current element has a following sibling with a local name matching the current local name and ending with Unit

<xsl:when test="following-sibling::node()[name()=concat($cName,'Unit')]">

the current node has to be a node containing the amount.
The value of the current node is written as value of the amount attribute

<xsl:attribute name="amount">
    <xsl:value-of select="."/>
</xsl:attribute>

and in case a following sibling with matching Percent exists

<xsl:if test="following-sibling::node()[name()=concat($cName,'Percent')]">

the Percent attribute is written accordingly:

<xsl:attribute name="percent">
    <xsl:value-of select="following-sibling::node()[name()=concat($cName,'Percent')]"/>
  </xsl:attribute>

Same applies to Unit without previously checking if a matching Unit exists (which could be added if necessary).
The empty

<xsl:when test="contains(name() ,'Unit') or contains(name() ,'Percent')"/>

removes the Unit and Percent nodes that has been written as attributes as well as the cholesterolUnit.
Finally, all other non groupable nutrition elements are just copied:

<xsl:otherwise>
  <xsl:copy>
    <xsl:apply-templates/>
  </xsl:copy>
</xsl:otherwise>