I can suggest several approaches, but I don't guarantee that any of them
will perform better than doing the repeated (wasteful) tokenization.
(1) Do a preprocessing pass in which you split the data attribute into
multiple elements, then proceed "as normal".
(2) Do a preprocessing pass to compute a sequence of NxM strings in one big
sequence, then operate by indexing into this big sequence.
(3) Write a user-defined function that calls tokenize() but with
saxon:memo-function="yes", so that the results of tokenizing a node are
remembered when you tokenize the same node again.
I think I would probably go for (2) as it's simplest:
<xsl:variable name="bigArray" select="for $x in Line return
tokenize($x/@data, '\s')"/>
<xsl:variable name="columns" select="count(Line)"/>
<xsl:for-each select="1 to xs:integer(@samples)">
<xsl:variable name="row" select="."/>
<tr>
<xsl:for-each select="1 to $columns">
<xsl:variable name="col" select="."/>
<td><xsl:value-of select="$bigArray[(:some function of $row and
$column, an exercise for the reader:)]
Michael Kay
http://www.saxonica.com/
-----Original Message-----
From: Beldaz Jalfrezi [mailto:beldazj(_at_)yahoo(_dot_)com(_dot_)au]
Sent: 04 November 2008 23:13
To: xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com
Subject: [xsl] Efficently transposing tokenized data
Hi XSL-List members,
I have been learning my way around XSLT (2.0) over the past
couple of weeks, principally using Saxon-B 9.1. I have an
immediate need to transform existing XML data, initially to
HTML. The XML contains, similar to SVG, space-tokenized
numerical data held within attributes. What I am having
trouble understanding is how to transform several nodes with
such data into individual columns of data.
The XML is like this:
<MultiLine samples="5">
<Line title="Line 1" data="0.1 0.4 0.6 0.4 0..8" /> <Line
title="Line 2" data="0.4 0.2 0.5 1.4 3.8" /> </MultiLine>
There can be any number of <Line> nodes (typically 3 or 4)
and the number of values (samples) in each data attribute for
each <Line> must match the samples attribute of the parent
<MultiLine> node. The number of samples can be very long,
typically several thousand. At present this is the data that
I am being supplied, so regardless of any shortcomings of the
structure (although suggestions for improvement are welcome)
I am stuck with it.
I want to transform such data into, e.g., HTML columns, like:
<TABLE>
<TR>
<TH>Line 1</TH><TH>Line 2</TH>
</TR>
<TR>
<TD>0.1</TD><TD>0.4</TD>
</TR>
<TR>
<TD>0.4</TD><TD>0.2</TD>
</TR>
<TR>
<TD>0.6</TD><TD>0.5</TD>
</TR>
...
</TABLE>
I have seen similar questions where people have wanted to
transpose HTML table data, but the problem here is that the
input data has to be tokenized. I can output the data
sequentially for each Line with a template such as:
<xsl:template match="Line">
<TR><TH><xsl:value-of select="@title" /></TH><TR>
<xsl:for-each select="tokenize(@data,' ')">
<TR><TD>
<xsl:value-of select="position()" />
</TD></TR>
<xsl:value-of select="." />
</xsl:for-each>
</xsl:template>
To format the data as adjacent columns the only approach I
can think of is a for-each loop over the number of samples,
and in each case call index-at(tokenize(../Line[n]/@data, '
'), position()) for each Line. But this looks horribly
inefficient, since I appear to be tokenizing every @data
attribute repeatedly, presumably giving complexity
O(count(Line)*samples^2). What would be far more preferable
is to tokenize all the lines, and then at each index obtain
the appropriate value from each sequence. But I have no idea
how to do that in XSLT.
I have spent at least a day trying to solve this conumdrum,
so if anyone has any suggestions I would be very grateful.
Kind regards,
Beldaz
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