[NTG-context] Xml filtering in Lua

[Hans Hagen]

On 11/16/2022 8:56 PM, mf via ntg-context wrote:
> This works:
> 
> local metadata = xml.filter (t, '../../topics/topic[@t:id=="' .. ch_id 
> .. '"]')
> 
> also this:
> 
> local lpath = string.format('../../topics/topic[@t:id=="%s"]', ch_id)
> 
> local metadata = xml.filter (t, lpath)
> 
> 
> It looks like xml.filter supports only 2 arguments (see lxml-tex.lua), 
> and so it doesn't let you use string formatting patterns like the 
> "context" command does.
> 
> You can write:
> 
> context('the value of @t:id is "%s"', ch_id)
> 
> but you can't write:
> 
> xml.filter (t, '../../topics/topic[@t:id=="%s"]', ch_id)
In Thomas example this is also an approach:

\startxmlsetups xml:document
	\xmlfunction{#1} {document}
  	\xmlflush{#1}
\stopxmlsetups

with

\startluacode
local topics   = { }
local chapters = { }

function xml.functions.document(t)
     for c in xml.collected(t,"/topics/topic") do
         topics[c.at.t_id] = c
     end
  -- for c in xml.collected(t,"/chapters/chapter") do
  --     chapters[c.at.ch_id] = c
  --     -- or flush here
  -- end
end

function xml.functions.chapter (t)
     local ch_id = t.at.ch_id
     local metadata = topics[ch_id]
     lxml.command(t, ".", "xml:chapter:content")
     context.par ()
     context (ch_id)
     context.par ()
end
\stopluacode

so, basically you collect data and use it later ... for huge datasets 
that saves some time

if you have only chapters to process you can even decide to flush in 
that function

Hans

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