Deduplicate and merge memory XML - xslt

Question

I have /credit-entity.xml (target)
<credit>
<entity>
<quality>Investment Grade</quality>
<outlook>Positive</outlook>
<LT-CRR>Aa3</LT-CRR>
<UUID>207</UUID>
<issuer>AA Bank NV</issuer>
<segment>Financial Institutions</segment>
<sector>Bank</sector>
</entity>
<entity>
<quality>Investment Grade</quality>
<outlook>Stable</outlook>
<LT-CRR>Aa3</LT-CRR>
<UUID>203</UUID>
<issuer>GS Bank Europe SE</issuer>
<segment>Financial Institutions</segment>
<sector>Securities & Exchanges</sector>
<date>2022-02-17</date>
<rating>A2</rating>
</entity>
<entity>
<quality>Investment Grade</quality>
<outlook>Stable</outlook>
<ST>(P)P-2</ST>
<UUID>118</UUID>
<issuer>RMGS Services GmbH</issuer>
<segment>Corporates</segment>
<sector>Pharmaceuticals</sector>
<date>2021-12-22</date>
<rating>A2</rating>
</entity>
</credit>
/credit-rating.xml (source)
<ratings>
<rating>
<UUID>207</UUID>
<issuer>AA Bank NV</issuer>
<date>2022-02-07</date>
<rating>Aa3</rating>
</rating>
<rating>
<UUID>203</UUID>
<issuer>GS Bank Europe SE</issuer>
<date>2022-01-31</date>
<rating>A1</rating>
</rating>
<rating>
<LT>A2</LT>
<LT-Type>LT Counterparty Risk Rating - Fgn Curr</LT-Type>
<UUID>233</UUID>
<issuer>AHR AG - Public sector Pfandbriefe</issuer>
<segment>Financial Institutions</segment>
<sector>Covered Bonds</sector>
<date>2022-01-25</date>
<rating>A3</rating>
</rating>
<rating>
<UUID>118</UUID>
<issuer>RMGS Services GmbH</issuer>
<date>2022-02-24</date>
<rating>A1</rating>
</rating>
</ratings>
My xsl is to:
-) match /ratings/rating/UUID with /credit/entity/UUID. If there is matched UUID, compare and get the latest date, create a new element latest with the UUID’s latest date and rating.
-) If no matched UUID in /credit-rating.xml, move its date and rating to form the new element latest.
-) If UUID is in source /credit-rating.xml but missing in target /credit-entity.xml, e.g. UUID 233. Then copy /ratings/rating to target and create new element latest with its date and rating.
Expected output:
<credit>
<entity>
<quality>Investment Grade</quality>
<outlook>Positive</outlook>
<LT-CRR>Aa3</LT-CRR>
<UUID>207</UUID>
<issuer>AA Bank NV</issuer>
<segment>Financial Institutions</segment>
<sector>Bank</sector>
<latest>
<date>2022-02-07</date>
<rating>Aa3</rating>
</latest>
</entity>
<entity>
<quality>Investment Grade</quality>
<outlook>Stable</outlook>
<LT-CRR>Aa3</LT-CRR>
<UUID>203</UUID>
<issuer>GS Bank Europe SE</issuer>
<segment>Financial Institutions</segment>
<sector>Securities & Exchanges</sector>
<latest>
<date>2022-02-17</date>
<rating>A2</rating>
</latest>
</entity>
<entity>
<quality>Investment Grade</quality>
<outlook>Stable</outlook>
<ST>(P)P-2</ST>
<UUID>118</UUID>
<issuer>RMGS Services GmbH</issuer>
<segment>Corporates</segment>
<sector>Pharmaceuticals</sector>
<latest>
<date>2022-02-24</date>
<rating>A1</rating>
</latest>
</entity>
<entity>
<LT>A2</LT>
<LT-Type>LT Counterparty Risk Rating - Fgn Curr</LT-Type>
<UUID>233</UUID>
<issuer>AHR AG - Public sector Pfandbriefe</issuer>
<segment>Financial Institutions</segment>
<sector>Covered Bonds</sector>
<latest>
<date>2022-01-25</date>
<rating>A3</rating>
</latest>
</entity>
</credit>
But somehow my code didn’t work. Can anyone help to fix the issue?
<xsl:variable name="ratingEntity" select="doc('/credit-rating.xml')/ratings/rating"/>
<xsl:variable name="ID">
<xsl:sequence select="credit/entity/UUID"/>
</xsl:variable>
<xsl:template match="credit">
<xsl:copy>
<xsl:for-each select="entity">
<xsl:variable name="uuid" select="UUID"/>
<xsl:copy>
<xsl:choose>
<xsl:when test="not(exists(rating)) or date le $ratingEntity[UUID eq $uuid]/date" >
<xsl:copy-of select="./* except (date, rating)"/>
<latest>
<xsl:call-template name="latest">
<xsl:with-param name="ratingEntity" select="$ratingEntity[UUID eq $uuid]" />
</xsl:call-template>
</latest>
</xsl:when>
<xsl:otherwise>
<xsl:copy-of select="./* except (date, rating)"/>
<latest>
<xsl:copy-of select="."/>
</latest>
</xsl:otherwise>
</xsl:choose>
</xsl:copy>
</xsl:for-each>
<xsl:call-template name="missing">
<xsl:with-param name="ratingEntity" select="$ratingEntity[$ID ne UUID]" />
</xsl:copy>
</xsl:template>
<xsl:template name="missing">
<xsl:param name="ratingEntity"/>
<entity>
<xsl:copy-of select="$ratingEntity"/>
</entity>
</xsl:template>
<xsl:template name="latest">
<xsl:param name="ratingEntity"/>
<xsl:copy-of select="$ratingEntity except (UUID, issuer)"/>
</xsl:template>

Answer 1

I think you simply want
<xsl:template match="credit">
<xsl:copy>
<xsl:for-each-group select="entity, doc('/credit-rating.xml')/ratings/rating" group-by="UUID">
<entity>
<xsl:apply-templates select="* except (date, rating)"/>
<lastest>
<xsl:variable name="max-date" select="max(current-group()/xs:date(date))"/>
<date>{$max-date}</date>
<rating>{current-group()[date = $max-date]/rating}</rating>
</lastest>
</entity>
</xsl:for-each-group>
</xsl:copy>
</xsl:template>