Re: [xsl] how to make a group-by multiple attributes motionless

["Geert Bormans geert@xxxxxxxxxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Thank you Michael, the copy-of() used this way makes perfect sense. 
Works like a charm now, thanks a lot 

Met vriendelijke groeten, 
Best regards, 

Geert Bormans 


Van: "Abel Braaksma, (Exselt) abel@xxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> 
Aan: "xsl-list" <xsl-list@xxxxxxxxxxxxxxxxxxxxxx> 
Verzonden: Donderdag 26 september 2019 00:55:50 
Onderwerp: Re: [xsl] how to make a group-by multiple attributes motionless 

This code passes Saxon's streamability tests: 

<xsl:stylesheet version = "3.0" xmlns:xs = " [ http://www.w3.org/2001/XMLSchema | http://www.w3.org/2001/XMLSchema ] " 
xmlns:xsl = " [ http://www.w3.org/1999/XSL/Transform | http://www.w3.org/1999/XSL/Transform ] " > 

<xsl:mode streamable = "yes" /> 

<xsl:template match = "/" > 
<out> 
<xsl:fork> 
<xsl:for-each-group select = "/*/row" group-by = "((@* => copy-of() => sort((), function($x){name($x)})) ! (name() || '=' || string(.))) => string-join(' ')" > 
<xsl:sequence select = "current-group()" /> 
</xsl:for-each-group> 
</xsl:fork> 
</out> 
</xsl:template> 
</xsl:stylesheet> 

Note that the sort() function requires XPath 3.1 so its streamability analysis isn't covered in the XSLT 3.0 spec, but Saxon applies similar rules to functions such as fn:filter: if the first argument is grounded then the function is streamable. 

The key here is the use of copy-of() to copy the attributes before sorting; this enables the compiler to know that the sort function isn't going to do any non-streamable navigation starting at the attribute node. In fact, after sorting you could equally well call a user-defined function that sorts using xsl:perform-sort. 

Michael Kay 
Saxonica 




On 25 Sep 2019, at 22:44, Geert Bormans [ mailto:geert@xxxxxxxxxxxxxxxxxxx | geert@xxxxxxxxxxxxxxxxxxx ] < [ mailto:xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx | xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx ] > wrote: 

All, 

I a streaming XSLT 3.0, I have to group a series of elements by their attribute names and values 
I have issues making the group-by motionless 

In a simplified example 

<rows> 
<row a="val-a-1" b="b-val"/> 
<row a="val-a-2" b="b-val"/> 
<row a="val-a-1" b="b-val"/> 
<row a="val-a-2"/> 
</rows> 

I need grouping this way 

<rowgroups> 
<rowgroup hash="|a=val-a-1|b=b-val"/> 
<rowgroup hash="|a=val-a-2|b=b-val"/> 
<rowgroup hash="|a=val-a-2"/> 
</rowgroups> 

easily achieved this way 

<xsl:fork> 
<xsl:for-each-group select="*" group-by="string-join(@*/concat('|', name(), '=', .), '')"> 
<rowgroup hash="{current-grouping-key()}"/> 
</xsl:for-each-group> 
</xsl:fork> 

but, I could have data like this (third line attribute order swapped) 

<rows> 
<row a="val-a-1" b="b-val"/> 
<row a="val-a-2" b="b-val"/> 
<row b="b-val" a="val-a-1"/> 
<row a="val-a-2"/> 
</rows> 

and this basically gives me a fourth group using the code above 

So I want to make sure that the attributes order can be controlled when I prepare the group-by, but any sorting attempt I make, leads to the group-by no longer being motionless 

I would welcome your suggestions 

Thanks 

Met vriendelijke groeten, 
Best regards, 

Geert Bormans 
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