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RE: Re: XSLT Subtract function?

Subject: RE: Re: XSLT Subtract function?
From: cknell@xxxxxxxxxx
Date: Fri, 13 Apr 2007 11:48:43 -0400
RE: Re:  XSLT Subtract function?
Thanks, Andrew. David Carlisle put me right. I can't evaluate a string as an XPath expression, which was (now that David has pointed out my error), not a legitimate approach.
-- 
Charles Knell
cknell@xxxxxxxxxx - email



-----Original Message-----
From:     Andrew Welch <andrew.j.welch@xxxxxxxxx>
Sent:     Fri, 13 Apr 2007 16:27:09 +0100
To:       xsl-list@xxxxxxxxxxxxxxxxxxxxxx
Subject:  Re:  XSLT Subtract function?

On 4/13/07, cknell@xxxxxxxxxx <cknell@xxxxxxxxxx> wrote:
> Yesterday I was tasked to produce a list of records from an Oracle database where the result set contained rows where the value in one of the columns was not one of a long list. (Bear with me, please, we'll get to XSLT in a moment.)
>
> The problem was that the list of values to omit was simply too long for SQL*Plus. So I went to plan B. I selected all the rows from the table in question into an XML document. I prepared a second XML document that contained an element for each of the values to be omitted.
>
> I then wrote a stylesheet with this template:
>
> <xsl:template match="ROWSET">
>   <ROWSET>
>     <xsl:apply-templates select="ROW[not(CODE = $active-codes/ROWSET/ROW/CODE)]" />
>   </ROWSET>
> </xsl:template>
>
> So the output contained all the ROW elements in the original document whose CODE child string value didn't match any of the CODE string values in the document containing the values I wanted to omit from the result.
>
> In short, I wanted to subtract the set of values contained in the second document from the first, resulting in a document containing only the non-matching values.
>
> After I finished, it occurred to me that this probably wasn't so unusual a need, and that probably someone had written a general-purpose function for this. What I had in mind is a function that would take four arguments:
>
> 1) A base document (base document) [$base]
> 2) A document containing the values to subtract from the base document (exemplar document) [$exemplar]
> 3) The XPath to the elment in the base document holding the values of interest. [$base-element]
> 4) The XPath to the element in the exemplar document holding the values of interest. [$list-element]
>
> The result would be a document with the same structure as the base document containing only those elements which didn't have a matching value.
>
> Here is an example of two documents:
>
> The base document:
>
> <?xml version="1.0"?>
> <grocery-list>
>   <item>apple</item>
>   <item>milk</item>
>   <item>cheese</item>
>   <item>coffee</item>
>   <item>asparagus</item>
> </grocery-list>
>
> The exemplar document:
>
> <?xml version="1.0"?>
> <inventory>
>   <sku>apple</sku>
>   <sku>pear</sku>
>   <sku>grapes</sku>
> </inventory>
>
> What I would like is a general-purpose function that would subtract those elements from the first document whose values matched the elements in the second.
>
> <grocery-list>
>   <item>milk</item>
>   <item>cheese</item>
>   <item>coffee</item>
>   <item>asparagus</item>
> </grocery-list>
>
> I've poked around on Google, but haven't found a useful was to compose the search. Does anyone on the list know of such a function or have you written one? I am reluctant to re-invent the wheel, particularly when mine is not likely to be as round and smooth as an existing one.

Is this any good?

select="$base//item[not(. = $exemplar//sku)]"

cheers
andrew

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