XSLT Muenchian sorting - xslt

Question

I'm trying to get a better understanding of the Muenchian grouping. I'm restricted to XSL 1.0. I was able to do groupings by attributes but I can't seem to get a grouping by element value to work.
My XML looks like this:
<?xml version="1.0"?>
<orders>
<order date="2015-01-01">
<product amount="8">Apple</product>
<product amount="1">Pear</product>
</order>
<order date="2015-01-01">
<product amount="1">Plum</product>
<product amount="5">Pear</product>
</order>
<order id="01" date="2015-01-03">
<product amount="10">Pear</product>
<product amount="4">Plum</product>
</order>
</orders>
What I'm trying to achieve is building a SVG diagram which shows how many of each fruit were ordered. So that one can easily see which is the top selling fruit per example. This would look like this (NOTE the amount-numbers are not resembling the XML above):
diagram: group by product
The code that I came up with so far is the following:
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:svg="http://www.w3.org/2000/svg" >
<xsl:variable name="baseline" select="480"/>
<xsl:key name="group-by-product" match="product" use="." />
<xsl:template match="/orders">
<svg:svg >
<svg:g>
<xsl:apply-templates select="order/product[generate-id(.)=generate-id(key('group-by-product',.)[1])]" />
<!-- draw x- axis and y - axis -->
<svg:path style="stroke-width:2; stroke:black" >
<xsl:attribute name="d">
<xsl:text>M 40 100 L 40 </xsl:text>
<xsl:value-of select="480"/>
<xsl:text> L </xsl:text>
<xsl:value-of select="2* count(order) * 40 + 80" />
<xsl:text> </xsl:text>
<xsl:value-of select="$baseline"/>
<xsl:text> L 40 </xsl:text>
<xsl:value-of select="$baseline"/>
<xsl:text> Z</xsl:text>
</xsl:attribute>
</svg:path>
</svg:g>
</svg:svg>
</xsl:template>
<xsl:template match="order">
<xsl:variable name="y" select="sum(key('order-by-product',product)/#amount)"/>
<svg:rect x="{40 * position()+20}" y="{$baseline - $y}" width="30" height="{$y}" style="fill:blue"/>
<svg:text style="writing-mode:tb" x="{41 * position()+20}" y="{$baseline - $y - 10}">
<xsl:value-of select="$y" />
</svg:text>
<svg:text style="writing-mode:tb" x="{41 * position()+15}" y="{$baseline + 20}">
<xsl:value-of select="product" />
</svg:text>
</xsl:template>
</xsl:stylesheet>
I feel like I have some inconsistencies in my code and confused myself with all the different examples I already looked at..
If possible I would like to avoid "for-each" and use "apply-template" instead.
Thank you for your help!

Answer 1

You've got the Muenchian grouping logic right, but the template wrong - your apply-templates selects product elements:
<xsl:apply-templates select="order/product[generate-id(.)=generate-id(key('group-by-product',.)[1])]" />
but your second template matches order elements so it will never fire. You need to change it to something like
<xsl:template match="product">
<xsl:variable name="y" select="sum(key('order-by-product',.)/#amount)"/>
<svg:rect x="{40 * position()+20}" y="{$baseline - $y}" width="30" height="{$y}" style="fill:blue"/>
<svg:text style="writing-mode:tb" x="{41 * position()+20}" y="{$baseline - $y - 10}">
<xsl:value-of select="$y" />
</svg:text>
<svg:text style="writing-mode:tb" x="{41 * position()+15}" y="{$baseline + 20}">
<xsl:value-of select="." />
</svg:text>
</xsl:template>