On 9/11/05, Michael Kay <mike(_at_)saxonica(_dot_)com> wrote:
This kind of problem is best tackled using recursion. It's difficult to
write your first recursive stylesheet, but it's a very powerful technique to
have under your belt.
Basically you need to write a template that processes one of the siblings,
passing it the value of your "counter" or "running-total" as a parameter.
The template needs to make whatever changes are necessary to the counter or
running total, then make a recursive call to process the next element if
there is one, passing the new value of the counter or running total as a
parameter. When the final sibling is reached, you return (or write to the
output) the final value of the counter.
You can do this either with call-template or apply-templates (perhaps using
a special mode). I find it easier to use apply-templates, for two reasons:
(a) the current node is passed as an implicit parameter, and (b) the
recursion often terminates naturally when there are no more siblings.
Here's an example that totals @price*(_at_)qty over a set of sibling elements:
<xsl:template match="order">
<total-value>
<xsl:apply-template select="order-item[1]">
<xsl:with-param name="running-total" select="0"/>
</xsl:apply-templates>
</total-value>
</xsl:template>
<xsl:template match="order-item">
<xsl:param name="running-total"/>
<xsl:choose>
<xsl:when test="following-sibling::order-item">
<xsl:apply-template select="following-sibling::order-item[1]">
<xsl:with-param name="running-total" select="$running-total +
(@price*(_at_)qty)"/>
</xsl:apply-templates>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="$running-total + (@price*(_at_)qty)"/>
</xsl:otherwise>
</xsl:choose>
</xsl:template>
Or using FXSL:
<xsl:value-of select=
"f:foldl(f:add(),
0,
f:zipWith(f:mult(),/*/*/@price, /*/*/@qty)
)"/>
Cheers,
Dimitre Novatchev
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