Get conditional value from previous node - xslt

Question

I have this XSLT 2.0 template:
<xsl:template match="footnote">
<xsl:variable name = "string" select="./text()"/>
<xsl:variable name = "bool">
<xsl:choose>
<xsl:when test="$string = preceding::footnote/text()">
<xsl:text>false</xsl:text>
</xsl:when>
<xsl:otherwise>
<xsl:text>true</xsl:text>
</xsl:otherwise>
</xsl:choose>
</xsl:variable>
<xsl:if test="$bool = 'true'">
<xsl:variable name="footnoteCount">
<xsl:call-template name="getItemNumber">
<xsl:with-param name="node" select="."/>
</xsl:call-template>
</xsl:variable>
<!-- DO XSL-FO TRANSFORMATION STUFF-->
</xsl:if>
<xsl:if test="$bool = 'false'">
<xsl:variable name = "footnoteCount">
<xsl:if test="$string = preceding::footnote/text()">
<xsl:value-of select="preceding::footnote/$footnoteCount"/>
</xsl:if>
</xsl:variable>
<!--DO XSL-FO TRANSFORMATION STUFF-->
</xsl:if>
</xsl:template>
Edited sample XML. I'd like to transform this:
<footnote>Foo bar</footnote>
<footnote>Bar foo</footnote>
<footnote>Foo bar</footnote>
<footnote>Foo bar</footnote>
<footnote>Bar</footnote>
<footnote>Foo</footnote>
Into this:
<footnote>Foo bar</footnote>
<footnote>Bar foo</footnote>
<footnote>Bar</footnote>
<footnote>Foo</footnote
And then stylise it using XSL-FO. The aim of this styling is that text in the main body will have a numbered reference, which is represented by $footnotecount, to the footnote which is then rendered at the bottom of the page. I need to transform the document so that duplicate footnates are only rendered once and that the number reference ($footnoteCount) is the same for each duplicate.
So what I'm trying to do with this template is:
Determine whether a footnote element with the current node's text already exists.
If it doesn't exist (i.e, '$bool' is 'true') , find the previous footnote's number, increment it (this is done in the 'getItemNumber' template) and create a 'new' footnote. If it does exist ($bool is 'false'), get the $footnoteCount variable of the node that the text matches and use it for the current node.
It's the scenario in which the footnote already exists that I'm having trouble with. I have no idea how to get the $footnoteCount variable from a previous, specific node dependent on whether than node meets a certain criteria (whether its text is the same as the $string variable in the current node). It's being made more difficult by the fact that the $footnoteCount variable only exists conditionally (even if in practice it will always exist since $bool has to be either true or false).
Does anyone have advice on what to do here?

Answer 1

This looks like a grouping problem, and in XSLT2.0 you can make use of the xsl:for-each-group element to get the distinct elements
<xsl:for-each-group select="footnote" group-by=".">
I think you need a different approach to do your numbering. Firstly you could create a variable to hold a 'look-up' of footnote descriptions and their index
<xsl:variable name="footnotes">
<xsl:for-each-group select="//footnote" group-by=".">
<footnote id="{position()}">
<xsl:value-of select="."/>
</footnote>
</xsl:for-each-group>
</xsl:variable>
This means the footnotes variable contains the following elements
<footnote id="1">Foo bar</footnote>
<footnote id="2">Bar foo</footnote>
<footnote id="3">Bar</footnote>
<footnote id="4">Foo</footnote>
Then, to replace your existing footnote elements with numeric references, you would have a template like this
<xsl:template match="footnote">
<footnote>
<xsl:value-of select="$footnotes/footnote[. = current()]/#id"/>
</footnote>
</xsl:template>
Try the following XSLT
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" indent="yes"/>
<xsl:variable name="footnotes">
<xsl:for-each-group select="//footnote" group-by=".">
<footnote id="{position()}">
<xsl:value-of select="."/>
</footnote>
</xsl:for-each-group>
</xsl:variable>
<xsl:template match="/*">
<xsl:apply-templates select="footnote"/>
Footnotes
<xsl:copy-of select="$footnotes"/>
</xsl:template>
<xsl:template match="footnote">
<footnote>
<xsl:value-of select="$footnotes/footnote[. = current()]/#id"/>
</footnote>
</xsl:template>
</xsl:stylesheet>
When applied to your sample XML (assuming a root element), the following is output
<footnote>1</footnote>
<footnote>2</footnote>
<footnote>1</footnote>
<footnote>1</footnote>
<footnote>3</footnote>
<footnote>4</footnote>
Footnotes
<footnote id="1">Foo bar</footnote>
<footnote id="2">Bar foo</footnote>
<footnote id="3">Bar</footnote>
<footnote id="4">Foo</footnote>

Answer 2

As well as failing to use xsl:for-each-group, there are many other things wrong with your code. For example, take this:
<xsl:variable name = "bool">
<xsl:choose>
<xsl:when test="$string = preceding::footnote/text()">
<xsl:text>false</xsl:text>
</xsl:when>
<xsl:otherwise>
<xsl:text>true</xsl:text>
</xsl:otherwise>
</xsl:choose>
</xsl:variable>
You can write that as
<xsl:variable name="bool" as="xs:boolean()"
select="$string = preceding::footnote"/>
Then you do this:
<xsl:if test="$bool = 'true'">
<xsl:variable name="footnoteCount">
<xsl:call-template name="getItemNumber">
<xsl:with-param name="node" select="."/>
</xsl:call-template>
</xsl:variable>
</xsl:if>
which is completely useless: the variable goes out of scope as soon as it is declared, so it can never be referenced.
You need to do some background reading about XSLT, there are a lot of ideas you haven't yet grasped.