Re: [xsl] Preferred declarative approach for outputting tallies based on complex triggers

[David Carlisle <davidc@xxxxxxxxx>]

On 10/04/2014 12:44, David Rudel wrote:
> After I wrote that post I realized that, in some sense, I might be
> asking the wrong question... Might one claim that if I'm still talking
> about "state variables" and the like that I'm not really embracing the
> declarative paradigm anyway?


Well quite I was going to ask what you mean by
"declarative/non-declarative and "updating state variables" in an XSLT
system.


> Perhaps I should be asking myself "How do
> I do the analysis I want to do without resorting to a subsystem of
> triggers and state functions?"
>
> I suppose one step in that direction would be to reduce dependence on
> triggers (at least) by using different values for the @mode attribute.
> Perhaps this would extend to reducing the number of state variables in
> general that I kept track of.
>
> To give a specific example question, consider a source with the
> following format:
>
> <items>
> <item id="31" value="3"/>
> <item id="21" value="1"/>
> ....
> </items>
>
> Each <item> element has an @id and an @value. There can be duplicates
> of both. An example question to answer is: "Given a set of @id values,
> an item is "special" if it has one of the @ids in this set AND it is
> the first such item with that particular @id. Find the subsequence of
> <items> lying between the first "special" item (if any) and the last
> special item (if any). For this subsequence, return various values
> like "how many total items are in the subsequence?" "How many
> 'special' items are in this subsequence?" "What is the average @value
> for all items in this subsequene? What is the average @value for the
> 'special' values? ...


I'd do something like something (untested)

<xsl:variable name="sids" select="31,35"/>
<xsl:variable name="a" select="(item[1],item[@id=$sids][1])[last()]"/>
<xsl:variable name="b" 
select="(item[last()],item[@id=$sids][last()])[last()]"/>
<xsl:variable name="s" select="$a|item[$a&lt;&lt;.][.&lt;&lt;$b]|$b"/>

no of items <xsl:value-of select="count($s)"/>
no of specials <xsl:value-of select="count($s[@id=$sids])/>
avg  <xsl:value of select="sum($s/@value) div count($s)"/>

I'm not sure what part you'd consider to be "triggers" or "state variables"

David