I have seen and used the <xsl:variable name="PrevPos" 
select="position() - 1" /> through trial and error, but I have not really 
understood why exactly this is. I read the explanation provided by Marrow 
but it seems to have gone over my head.



"Jason Burr" <JasonBurr@d...> wrote in message 
news:DD97D787-424F-4D74-B742-C69F5084D333@m......
> Marrow,
>
> Thanks simply assigning  variable worked (never tried that because of all
> the "no variable reassignment" griping)
>
> My thinking on the predicate was that the order of execution would be
>
> 1. evaluate value of the (current) position()-1
> 2. assign that value to position()
> 3. retrive the node given the assigned position
>
> I guess my thinking was that = doesn't evaluate the truth a statement such 
> as
>
> x = x + 1
>
> But rather
>
> (newvalue of x <--- (x - 1))
>
> Anyway good stuff to know thanks again.
>
> "Marrow" wrote:
>
>> Hi Jason,
>>
>> > Not trying to accomplish any thing was just messing around and thought
>> that
>> > it might be a good way to check for the last record in a group during a
>> loop.
>> > Since I can't reassign variables and position() tells me where in a 
>> > loop I
>> am
>> > and position() can also be used to specify a node to look up it seemed
>> (maybe
>> > foolishly) that this was an easy way to know if the current node and
>> previous
>> > node for a given value match.
>>
>> The position() function when used **outside** a predicate will give you 
>> the
>> position within the currently processed node-set (e.g. that selected by a
>> @select on <xsl:apply-templates> or <xsl:for-each>).  When the position()
>> function is used **within** a predicate then it ruturns the index of the
>> node within the nodes selected by the XPath expression to the left of the
>> predicate.
>>
>> Your problem remains...
>>
>> >   <xsl:when test="/foo/bar[position()=position()-1]/@attrib">
>>
>> read the bit inside the [] predicate! ;)
>>
>> How can "position()=position()-1" ever evaluate to true???  It can't... x
>> can never equal (x - 1)... complete impossibility!  ;)
>>
>> Maybe one of those position()'s is the position prior to the predicate? 
>> In
>> which case you would need to store one to a variable first, e.g something
>> like...
>>
>>  <xsl:for-each select="bar">
>>    <xsl:variable name="curr-posn" select="position()"/>
>>    <xsl:choose>
>>    <xsl:when test="/foo/bar[position()=$curr-posn -1]/@attrib">
>>       ...
>>
>> or even just calc the index, e.g.
>>
>>  <xsl:for-each select="bar">
>>    <xsl:variable name="prev-posn" select="position() - 1"/>
>>    <xsl:choose>
>>    <xsl:when test="/foo/bar[$prev-posn]/@attrib">
>>       ...
>>
>> Cheers
>> Marrow
>>
>> "Jason Burr" <JasonBurr@d...> wrote in message
>> news:C68421B0-71EE-4519-B453-EEB0735C5504@m......
>> > Hey Marrow,
>> >
>> > Not trying to accomplish any thing was just messing around and thought
>> that
>> > it might be a good way to check for the last record in a group during a
>> loop.
>> > Since I can't reassign variables and position() tells me where in a 
>> > loop I
>> am
>> > and position() can also be used to specify a node to look up it seemed
>> (maybe
>> > foolishly) that this was an easy way to know if the current node and
>> previous
>> > node for a given value match. I am aware of Muenchian (you may have 
>> > helped
>> me
>> > out with that).
>> >
>> > Anyway the context of that example would have been in
>> >
>> > <foo>
>> >   <bar attrib='test'>
>> >   <bar attrib='test'>
>> >   <bar attrib='test2'>
>> > </foo>
>> >
>> > <xsl:for-each select="bar">
>> >   <xsl:choose>
>> >   <xsl:when test="/foo/bar[position()=position()-1]/@attrib">
>> >    <xsl:value-of select="@attrib"/>
>> >   </xsl:when>
>> >   <xsl:otherwise>
>> >     <xsl:value-of select="@attrib"/> end of group
>> >   </xsl:otherwise>
>> >   </xsl:choose>
>> > </xsl:for-each>
>> >
>> > Result expected
>> >
>> > test
>> > test end of group
>> > test2
>> >
>> > Clearly I didn't mess with the keys or anything for grouping but this
>> would
>> > work if the xml was ordered or if using the Muenchian Technique. (that 
>> > is
>> if
>> > it evaluated like it does when using value-of)
>> >
>> > As far as it evaluating to nothing thats not completely true becuase if 
>> > I
>> > hard code in the value of the position
>> >
>> > <xsl:value-of select="/foo/bar[position()=3]/@attrib"/>
>> >
>> > The the result would be
>> >
>> > test2
>> >
>> > and if I do
>> >
>> > <xsl:value-of select="position()-1"/>
>> >
>> > I would get
>> >
>> > 0
>> > 1
>> > 2
>> >
>> > So my general question was why would that not evaluate to the value of 
>> > the
>> > node (which does exist) and return the value requested. Further if 
>> > there
>> is
>> > no way for this to work then is there another way to evaluate the same
>> thing
>> > (the previous node processed in a for-each)
>> >
>> > Thanks,
>> >
>> > Jason
>> >
>> >
>> >
>> > "Marrow" wrote:
>> >
>> > > Hi Jason,
>> > >
>> > > > But that this never returns a result
>> > > >
>> > > > <xsl:value-of select="/foo/bar[position()=position()-1]/@attrib"/>
>> > >
>> > > Of course it won't ever return anything...  the predicate [] 
>> > > expression
>> can
>> > > never evalaute to true.
>> > >
>> > > > What I want to do here is look at the last record in a loop to see 
>> > > > if
>> I am
>> > > > at the end of a grouping (begininig of the next actually)
>> > >
>> > > Based on what you have described so far (but not seeing more of the 
>> > > XSLT
>> and
>> > > XML) I'd say it'is unlikely that your current method of doing 
>> > > grouping
>> will
>> > > work.  There are a couple of ways of doing grouping in XSLT 1.0 - the
>> > > Muenchian Technique and preceding-sibling technique.  I'm sure if you
>> post
>> > > an example of what your are trying to do someone will be able to show
>> you
>> > > how to do these.
>> > >
>> > > Cheers
>> > > Marrow
>> > > http://www.marrowsoft.com - home of Xselerator (XSLT IDE and 
>> > > debugger)
>> > > http://www.topxml.com/Xselerator
>> > >
>> > >
>> > > "Jason Burr" <JasonBurr@d...> wrote in message
>> > > news:3CEE074F-AD95-4124-ADD2-8DB46106D9BA@m......
>> > > > Can someone explain why doing this writes a number one less than 
>> > > > the
>> > > current
>> > > > position.
>> > > >
>> > > > <xsl:value-of select="position()-1"/>
>> > > >
>> > > > Doing this will display a specific positions value
>> > > >
>> > > > <xsl:value-of select="/foo/bar[position()=3]/@attrib"/>
>> > > >
>> > > > But that this never returns a result
>> > > >
>> > > > <xsl:value-of select="/foo/bar[position()=position()-1]/@attrib"/>
>> > > >
>> > > > What I want to do here is look at the last record in a loop to see 
>> > > > if
>> I am
>> > > > at the end of a grouping (begininig of the next actually)
>> > > >
>> > >
>> > >
>> > >
>>
>>
>>