From: Jeff Nyman <jeffnyman_nospam@..._gmail.com>
Date: 2006-10-06T21:25:15+09:00
Subject: Re: Parse and modify an XML file with REXML

"Peter Szinek" <peter@rubyrailways.com> wrote in message 
news:45257DBC.20609@rubyrailways.com...
> jeffnyman@gmail.com wrote:
>> Greetings all.
>>
>> When processing XML, is there a way to check what the previous and what
>> the next "rows" are?
>
> I don't know REXML that much (and using Hpricot anyway ;-) but standard
> XPath axes ( following-sibling, preceding-sibling ) won't help? The
> previous node in this case would be self::previous-sibling[1] etc.

Thanks for the suggestion. This sounds like it might work. I did not see 
this in the REXML documentation initially but I see generally how these work 
in concept. In practice, it does not seem to work for me.

I have my XML like this (greatly pared down):

<perflog>
    <module>
        <perfpoints>
            <variable name="202G_OrdAdd">
            <variable name="203G_OrdUpdate">
            ....
        </perfpoints
    </module>
</perflog>

I tried this:

<code>
xml = Document.new(File.open("test.xml"))

events = XPath.match(xml,
   '/perflog/module/perfpoints/variable[@name="203G_OrdUpdate"]'
)

events.each do |event|
   puts XPath.match(event, '[self:preceding-sibling[1](@name, 
"202G_OrdAdd")]')
end
</code>

In the events iterator, I also tried the following variation:

puts XPath.match(event, 'self:preceding-sibling[1](@name, "202G_OrdAdd")')

I also tried replacing the 'self' with the full node path (i.e., 
"//perflog/module/perfpoints/variable").

I should note I don't get an error when I run the above. I simply get 
nothing, so my guess is that I'm using preceding-sibling wrong. I'm guessing 
it never feels it found the condition I'm indicating it should be finding.

I did find that I can do this:

puts XPath.match(event, '[self:preceding-sibling::variable[1](@name, 
"202G_OrdAdd")]')

(Note the "::variable[1]" addition.) Some documentation I found suggests 
that this should count backwards and reference the closest preceding 
variable sibling. That does seem to work -- to an extent, but I get 
everything returned. Meaning I get this in my results:

<variable name = "203G_OrdUpdate">
<variable name = "202G_OrdAdd">

... but then I get all the other 203's in my XML listed as well. What I'm 
trying to do is just return the one 203 that has a preceding sibling that 
has the attribute name 202G_OrdAdd.

I'm getting closer, though. Thank you for the suggestion, as this does seem 
to be the road I need to be on.

- Jeff