Re: union/intersection on attribute values
> DC, can you elaborate your approach using count()? 'tisn't really mine, but anyway in the beginning, the general method of gettin rid of duplicates (or equivalently getting the first item in each group of related items. was to go something like select="foo[not(.=preceeding::foo)]" ie select all foo's that don't have the same value as an earlier one. This works but has quadratic behaviour in the number of nodes being searched. Steve Meunch had an insight into using xsl:key to improve things. This is populatised by Jeni, who has a good description of it at her site. It's the method I used in my "dynamic" example. First you specify a key, then a node is the first item in a group 9ie the one you want if you are discarding duplicates) if it is the first node in the node set returned by the key. The only trick part is that XSL doesn't have a node identity test. Given a node $x and a node set $Y how do you tell if $x is in $Y. two basic methods, one uses generate-id to give strings which you can compare to give node identity test, the other uses set theory. count($x | $Y) is the number of elements in the set Y union the singlton set $x. This will be equal to count($Y) if $x is already in $Y and equal to count($Y)+1 otherwise. so... select="/records/record/*[count(.|key('x',name()))=1]"> selects all element child nodes of record for whic count(.|key('x',name()))=1 (rather than 2) ie it selects those nodes that are in the set key('x',name()) ie are the first node of each group. IE subsequent duplicates are not selected. David _____________________________________________________________________ This message has been checked for all known viruses by Star Internet delivered through the MessageLabs Virus Control Centre. For further information visit http://www.star.net.uk/stats.asp XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list
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