Re: Grouping data at multiple levels (can XSL do this?

Cheers,
Wendell

You've described your problem in very procedural terms, so it's not
surprising you are having trouble implementing it in a declarative
language. Your readers including me will have the same problem - reverse
engineering your requirements from an algorithm that doesn't work is not
easy.

If you show some sample input and output then we may be able to
recognize how they are related. If the relationship isn't obvious,
please try and explain it. Usually if you express the problem in terms
of rules like "this element in the output depends on these things in the
input" then an implementation in a functional language can be derived
from this without much difficulty.

Michael Kay
Saxonica

On 28/06/2011 19:47, Hank Ratzesberger wrote:

Hello,

I'm writing to this list for the first time because after using
XSL for some years I've come across a data pattern that I think
defies use by XSL. It is the kind of thing that a language that
allows you to alter/update variables and iterate through lists
can do with relative ease, but I don't find it possible with
XSL. It is an example of hierarchical meaning within flat
data, that is, there are groups of rows of data, but some
groups represent updates to information in prior groups.

In pseudo code, something like this

for each<receiver>
if (the<receiver> has a child<model-code>) then
create the element<myReceiverHistory> with all the children of
<receiver>
for each following-sibling of receiver that does not have a
<model-code> child
create a new<myReceiverHistory> by updating the most recent with
children info.

It is the kind of thing that loop construct with variables that
can be updated within the loop or that has a "continue" to
skip to the next, etc. can do.

Happy to be proved wrong or listen to your interest.

I can pull rows out of a database and put them into an xml format.
They are tidbits that, when sorted by date, create a group of changes
that occur on permanent GPS site. So, starting from this:

<result xmlns="">
<row>
<site-transaction-type>frequency standard</site-transaction-type>
<site-transaction-name>type</site-transaction-name>
<site-transaction-value>INTERNAL</site-transaction-value>
<effective-date>1990-01-09T00:00:00.000</effective-date>
</row>
<row>
<site-transaction-type>frequency standard</site-transaction-type>
<site-transaction-name>additional information</site-transaction-name>
<site-transaction-value>ROGUE SNR-8 uses external rubidium
standard</site-transaction-value>
<effective-date>1990-01-09T00:00:00.000</effective-date> </row>
<row>
...etc. etc.

I can use for-each-group to

<xsl:variable name="receivers">
<xsl:for-each-group
select="$transactions/row[site-transaction-type='receiver']"
group-by="effective-date">
<sopac:receiver xmlns:sopac="http://sopac.ucsd.edu/ns">
<xsl:copy-of select="current-group()"/>
</sopac:receiver>
</xsl:for-each-group>
</xsl:variable>

Which allows me to put all the things together that make up the actual
transaction. The catch is that only when one of the rows is a
"site-transaction-name" with the value 'model code' does it represent a
change to the receiver. Other changes, e.g. 'serial number' only
update the previous group of elements. The above creates this:

<sopac:receiver xmlns:sopac="http://sopac.ucsd.edu/ns">
<row xmlns="">
<site-transaction-type>receiver</site-transaction-type>
<site-transaction-name>model code</site-transaction-name>
<site-transaction-value>TRIMBLE 4000SST</site-transaction-value>
<effective-date>1990-02-09T00:00:00.000</effective-date>
</row>
<row xmlns="">
<site-transaction-type>receiver</site-transaction-type>
<site-transaction-name>firmware version</site-transaction-name>
<site-transaction-value>4.11</site-transaction-value>
<effective-date>1990-02-09T00:00:00.000</effective-date>
</row>
<row xmlns="">
<site-transaction-type>receiver</site-transaction-type>
<site-transaction-name>serial number</site-transaction-name>
<site-transaction-value>496</site-transaction-value>
<effective-date>1990-02-09T00:00:00.000</effective-date>
</row>
<row xmlns="">
<site-transaction-type>receiver</site-transaction-type>
<site-transaction-name>satellite system</site-transaction-name>
<site-transaction-value>GPS</site-transaction-value>
<effective-date>1990-02-09T00:00:00.000</effective-date>
</row>
<row xmlns="">
<site-transaction-type>receiver</site-transaction-type>
<site-transaction-name>additional information</site-transaction-name>
<site-transaction-value>First measurements</site-transaction-value>
<effective-date>1990-02-09T00:00:00.000</effective-date>
</row>
</sopac:receiver>
<sopac:receiver xmlns:sopac="http://sopac.ucsd.edu/ns">
<row xmlns="">
<site-transaction-type>receiver</site-transaction-type>
<site-transaction-name>serial number</site-transaction-name>
<site-transaction-value>422</site-transaction-value>
<effective-date>1990-02-14T00:00:00.000</effective-date>
</row>
<row xmlns="">
<site-transaction-type>receiver</site-transaction-type>
<site-transaction-name>sample interval</site-transaction-name>
<site-transaction-value>30</site-transaction-value>
<effective-date>1990-02-14T00:00:00.000</effective-date>
</row>
<row xmlns="">
<site-transaction-type>receiver</site-transaction-type>
<site-transaction-name>additional information</site-transaction-name>
<site-transaction-value>Site ties 05-MAR-1990</site-transaction-value>
<effective-date>1990-02-14T00:00:00.000</effective-date>
</row>
</sopac:receiver>

...

Even creating a variable with the necessary hierarchy is problematic
because I can't go back to get the data -- or maybe I can with
a tricky previous-sibling ?

Thanks,
Hank

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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
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