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Re: [xsl] Duplicate Elimination


Subject: Re: [xsl] Duplicate Elimination
From: David Carlisle <davidc@xxxxxxxxx>
Date: Thu, 13 Mar 2014 11:17:32 +0000

On 13/03/2014 10:59, Ihe Onwuka wrote:
e for-each syntax is more verbose.

Muenchian grouping is not something I burden my short term memory with because I hardly ever use it and and it's a phrase that is meaningless beyond a very select cognoscenti. What I posted can literally be described to a layman - add all the B/Dates that aren't in the set of A/Dates additionally it literally translates it into a set-theoretic

Not at all in an internet age, "muenchian grouping" might be an arbitrary label, but if you (or rather I) call it that rather than call it "the grouping idiom using keys that used to be needed in XSLT1" then you have a high probability of getting an exact description and code samples if you type it into google.



A union (B diff A)


That's why I prefer it.

But as I say if you have more than a dozen or so elements in your list you are likely to be able to observe the time difference.


this will (unless you have a very aggressively optimising XSLT engine) be quadratic in performance as the full A list is going to be searched for every B.


good point. If and when the volumes warrant performance tuning I'll know where to start.

Also of course using text() rather than

<xsl:apply-templates select="A/Date | B/Date[not(current()/A/Date =
.)]>

means the code is very fragile and will break if comments spit up
the text nodes.


I have been doing too much XQuery recently,



The same advice not to use text() applies equally to XQuery.



but is . robust against changes to the content model?

well you were already using it for sorting, and if if the content model changes then any of this could break. if Date became <Date><year>2014</date><moth>03</month><day>13</day></Date> then . would keep working but text() would break.

David





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