In the alphabetical list,
count($persNames[normalize-space(lower-case(.)) =$current-name])"/
could be optimized by:
(a) using keys
(b) using Saxon-SA which will optimize it to use a key automatically
(c) using xsl:for-each-group rather than distinct-values(), though that will
require some restructuring of your code.
In the frequency-sorted list, I think for-each-group would definitely be
better:
<xsl:for-each-group select="$persNames" group-by="lower-case(.)">
<xsl:sort select="count(current-group())"/>
...
(Note also the use of a case-blind collation rather than lower-case(),
discussed in another thread today)
Michael Kay
http://www.saxonica.com/
-----Original Message-----
From: James Cummings [mailto:cummings(_dot_)james(_at_)gmail(_dot_)com]
Sent: 08 February 2008 14:28
To: xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com
Subject: [xsl] distinct-values() optimization, sorting by frequency
Hiya,
I'm wondering the best way to optimize a distinct-values()
based transformation. What I'm basically doing is:
======
<xsl:variable name="docs"
select="collection('../../working/xml/files.xml')"/>
<xsl:template name="main" >
<xsl:variable name="persNames"
select="$docs//tei:text//tei:persName"/>
<xsl:variable name="norm-persNames"
select="$persNames/normalize-space(lower-case(.))"/>
<xsl:variable name="distinct-persNames"
select="distinct-values($norm-persNames)"/>
<!-- I realize that I could be more specific on the
$persNames variable, but doing so doesn't seem to affect
speed much at all. --> <div type="main">
<!-- Some overall counts -->
<div><head>Overall Counts</head>
<list type="unordered">
<item>Number of <gi>persName</gi> elements total:
<xsl:value-of select="count($persNames)"/></item>
<item>Number of <gi>persName</gi> elements which have a
@key attribute total: <xsl:value-of
select="count($persNames[(_at_)key])"/></item>
<item>Number of distinct-value <gi>persName</gi> elements total:
<xsl:value-of select="count($distinct-persNames)"/></item>
</list></div>
<!-- An Alphabetical List -->
<div><head>Alphabetical List</head>
<list type="unordered">
<xsl:for-each select="$distinct-persNames">
<xsl:sort select="."/>
<xsl:variable name="current-name" select="."/>
<xsl:variable name="count-distinct-current-name"
select="count($persNames[normalize-space(lower-case(.))
=$current-name])"/>
<item><xsl:value-of select="concat($current-name,
' -- ', $count-distinct-current-name)"/></item>
</xsl:for-each>
</list>
</div>
<!-- A Frequency Sorted List -->
<div>
<head>Frequency List</head>
<list type="unordered">
<xsl:for-each select="$distinct-persNames">
<xsl:sort
select="count($persNames[normalize-space(lower-case(.))
= .])"/>
<!-- I think it is this sort statement which slows things
down, since I have to repeat it twice. -->
<xsl:variable name="current-name" select="."/>
<xsl:variable name="count-distinct-current-name"
select="count($persNames[normalize-space(lower-case(.))
= $current-name])"/>
<item><xsl:value-of select="concat($count-distinct-current-name,
' -- ', $current-name)"/> </item>
</xsl:for-each>
</list>
</div>
</div>
======
I think the real slow-down comes in the second xsl:for-each
where I want to sort by frequency of distinct-value by doing:
<xsl:sort
select="count($persNames[normalize-space(lower-case(.)) =
.])"/> I have to have it for the sort, and then I have to
re-do it for the output inside the <item> element. I'm
obviously not allowed a variable between the for-each and the
sort... but I have a feeling I'm missing some clever
optimization here.
Although this is for a pre-generated transformation, it
currently takes a *hugely* long time, and I'm thinking I must
be able to optimize it somehow.
Any suggestions appreciated,
-James
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