Request for xml.filter explanation!

Request for xml.filter explanation!

[Geert Verhaag]

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Hi,

I've the following xml file:

*<?xml version='1.0' standalone='yes?>

<content>
  <object mid="a">
   <text>a paragraph of text</text>
   <value>40.2</value>
  </object>
  <object mid="b">
   <text>another paragraph of text</text>
   <value>10.7</value>
  </object>
  <object mid="c">
   <text>still another paragraph!</text>
   <value>20.5</value>
  </object>
</content>*

And want to calculate the total value of all the objects:

like so:

*\startxmlsetups xml:example:base
   \xmlsetsetup{#1}{content|object}{xml:example:*}
\stopxmlsetups

\xmlregisterdocumentsetup{example}{xml:example:base}

\startxmlsetups xml:example:content
totalvalue: \xmlfunction{#1}{totalvalue}
\xmlflush{#1} \endgraf
\stopxmlsetups

\startxmlsetups xml:example:object
attribute : \xmlatt{#1}{mid} \par
\stopxmlsetups

% LUA

\startluacode
function xml.functions.totalvalue(root)
local score = 0
for e in xml.collected(root,"/object") do
tex.write('Okay!')
--score = score + xml.filter(e,"xml:///value/number()") or 0
end
tex.write(score)
end
\stopluacode

\starttext

\xmlprocessfile{example}{content.xml}{}

\stoptext*

*
*

When I run this example I get:

*totalvalue: Okay!Okay!Okay!0 attribute : a
attribute : b
attribute : c*

That looks allright!

But when I incorporate the line:

*score = score + xml.filter(e,"xml:///value/number()") or 0*

the following Lua error is thrown:
**

*! LuaTeX error [string "\directlua "]:5: attempt to perform arithmetic 
on a nil value*

Has anybody any idea what I'm doing wrong here? The manual 
*xml-mkiv.pdf* doesn't give any clue about this!

Regards,
Gerard
-- 



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Re: Request for xml.filter explanation!

[Hans Hagen]

On 4/10/2019 9:27 PM, Geert Verhaag wrote:
> Hi,
> 
> I've the following xml file:
> 
> *<?xml version='1.0' standalone='yes?>
> 
> <content>
>   <object mid="a">
>    <text>a paragraph of text</text>
>    <value>40.2</value>
>   </object>
>   <object mid="b">
>    <text>another paragraph of text</text>
>    <value>10.7</value>
>   </object>
>   <object mid="c">
>    <text>still another paragraph!</text>
>    <value>20.5</value>
>   </object>
> </content>*
> 
> And want to calculate the total value of all the objects:
> 
> like so:
> 
> *\startxmlsetups xml:example:base
>    \xmlsetsetup{#1}{content|object}{xml:example:*}
> \stopxmlsetups
> 
> \xmlregisterdocumentsetup{example}{xml:example:base}
> 
> \startxmlsetups xml:example:content
> totalvalue: \xmlfunction{#1}{totalvalue}
> \xmlflush{#1} \endgraf
> \stopxmlsetups
> 
> \startxmlsetups xml:example:object
> attribute : \xmlatt{#1}{mid} \par
> \stopxmlsetups
> 
> % LUA
> 
> \startluacode
> function xml.functions.totalvalue(root)
> local score = 0
> for e in xml.collected(root,"/object") do
> tex.write('Okay!')
> --score = score + xml.filter(e,"xml:///value/number()") or 0
> end
> tex.write(score)
> end
> \stopluacode
> 
> \starttext
> 
> \xmlprocessfile{example}{content.xml}{}
> 
> \stoptext*
> 
> *
> *
> 
> When I run this example I get:
> 
> *totalvalue: Okay!Okay!Okay!0 attribute : a
> attribute : b
> attribute : c*
> 
> That looks allright!
> 
> But when I incorporate the line:
> 
> *score = score + xml.filter(e,"xml:///value/number()") or 0*
> 
> the following Lua error is thrown:
> **
> 
> *! LuaTeX error [string "\directlua "]:5: attempt to perform arithmetic 
> on a nil value*
> 
> Has anybody any idea what I'm doing wrong here? The manual 
> *xml-mkiv.pdf* doesn't give any clue about this!
\startluacode
     function xml.functions.totalvalue(root)
         local score = 0
         for e in xml.collected(root,"/object/value") do
             score = score + tonumber(xml.text(e)) or 0
         end
         context(score)
     end
\stopluacode


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___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
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wiki     : http://contextgarden.net
___________________________________________________________________________________