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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