xslt 1.0 add (conditional) tag only if previous tag is different - xslt

Question

I have the following source document;
<instance class-name="Deelnemer">
<attr attr-name="achternaam">
<value>McFly</value>
</attr>
<attr attr-name="geslacht">
<value>MAN</value>
</attr>
<attr attr-name="geboortedatum">
<value>1968-03-14</value>
</attr>
<attr attr-name="verzorgers">
<value>{"uuid":"f5a8fecd-7ea6-499e-a8a6-c6eb20e582b8","volgnummer":1}</value>
</attr>
<attr attr-name="verzorgers">
<value>{"uuid":"54748d2b-b2bf-4362-8520-4c4827a6660c","volgnummer":2}</value>
</attr>
</instance>
I transform it using this xslt (1.0);
<xsl:for-each select="./attr[#attr-name]">
<xsl:if test="string-length(.)"/>
<xsl:variable name="name" select="./#attr-name"/>
<xsl:variable name="value" select="normalize-space(./value)"/>
<modify-attr>
<xsl:attribute name="attr-name">
<xsl:value-of select="$name"/>
</xsl:attribute>
<remove-all-values/>
<add-value>
<value>
<xsl:value-of select="$value"/>
</value>
</add-value>
</modify-attr>
</xsl:for-each>
Which currently results in;
<modify-attr attr-name="geboortedatum">
<remove-all-values/>
<add-value>
<value>1968-03-14</value>
</add-value>
</modify-attr>
<modify-attr attr-name="verzorgers">
<remove-all-values/>
<add-value>
<value>{"uuid":"f5a8fecd-7ea6-499e-a8a6-c6eb20e582b8","volgnummer":1}</value>
</add-value>
</modify-attr>
<modify-attr attr-name="verzorgers">
<remove-all-values/>
<add-value>
<value>{"uuid":"54748d2b-b2bf-4362-8520-4c4827a6660c","volgnummer":2}</value>
</add-value>
</modify-attr>
But i want it to transform conditional if the previous tag (attribute) is the same as the current one.
<modify-attr attr-name="geboortedatum">
<remove-all-values/>
<add-value>
<value>1968-03-14</value>
</add-value>
</modify-attr>
<modify-attr attr-name="verzorgers">
<remove-all-values/>
<add-value>
<value>{"uuid":"f5a8fecd-7ea6-499e-a8a6-c6eb20e582b8","volgnummer":1}</value>
</add-value>
</modify-attr>
<modify-attr attr-name="verzorgers">
<add-value>
<value>{"uuid":"54748d2b-b2bf-4362-8520-4c4827a6660c","volgnummer":2}</value>
</add-value>
</modify-attr>
As seen by the "verzorgers" attr-name it appears twice but i only want a <remove-all-values> with the first occurrence of this tag/attr-name.
Tried several with currently the use of "preceding-siblings" to know the previous value of "attr-name" within the loop but the syntax keeps nagging me to result in usable code.
So helpful suggestions are more then welcome...

Answer 1

You could do:
<xsl:if test="not(#attr-name = preceding-sibling::attr[1]/#attr-name)">
<remove-all-values/>
</xsl:if>
Alternatively, you could define a key as:
<xsl:key name="attr-by-name" match="attr" use="#attr-name" />
and then do something along the lines of Muenchian grouping:
<xsl:if test="count(. | key('attr-by-name', #attr-name)[1]) = 1">
<remove-all-values/>
</xsl:if>
Note that the two are not the same: you will see a difference if the groups are not contiguous.