Subject: Re: [xsl] What does the phrase "duplicates removed" mean precisely? From: David Carlisle <davidc@xxxxxxxxx> Date: Wed, 1 Feb 2006 00:54:47 GMT |
Note that the terminology (and the facts) changes between XSLT1 and XSLT2 and your message refered to Michael Kay's 2.0 book, and Dave P's 1.0 FAQ. So I'll give two answers, but it would probably simplify things for you if you fixed on one or other version initially. a "node" is the generic term for all kinds of structured value in xpath, element nodes, attribute nodes, comment nodes etc. In XSLT1 the basic data type is a "node set" and sets by definition never have duplicates, so if you look at sets of integers, the set {1,3,1,1} is the same as the set {1,3} and has two members. Similarly in Xpath node sets if you (say) select the union of all the attributes, and one specific attribute select="@*|@this" then this is the same as just selecting all attributes select="@*" yiu don't get the attribute this="that" twice, just as the set {1,3,1,1} only has member equal to 1. In Xpath2 th ebasic data type is no longer a set but a sequence (that is an ordered lists) and if we again look at lists of integers the sequences (1,3) and (1,3,1,1) are different, one has length 2, and one has length 4,with 1 appearing threee times. given <foo this="that" a="b" c="d"/> so @*|@this again only contains the this="that" attribute once, although in xpath2 (unlike xpath1) you have the possibilty of having a sequence where it appears twice, for example select="@*,@this" > Are there any other kind of "duplicates" removed? Note that it is duplicates by _identity_ not by value. Given <x> <y>a</y> <y>a</y> </x> if the current node is x then select="y" will select both y element nodes, th efact that they have the same content doesn't make them duplicates. However of you select the same element twice for example select="y[last()]|y[2]" selects the second one twice in this case then this dupication is rempved and the result is a node set (in xpath1) or sequence (in xpath2) with just one y element. David ________________________________________________________________________ This e-mail has been scanned for all viruses by Star. The service is powered by MessageLabs. For more information on a proactive anti-virus service working around the clock, around the globe, visit: http://www.star.net.uk ________________________________________________________________________
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