Thank you, this worked perfectly after a few minor code fixes and after 
prepending # to the identifier.

For the convenience of those, who, like me, don't really know any Lua, I 
attach the fixed code.

local chapter_level = 2
local toc_level = 3
local headings = {}
local current_chapter = nil

local function collect_headings (head)
if head.level == chapter_level then
local id = head.identifier
current_chapter = {
chapter = id,
toc = {},
}
headings[id] = current_chapter
elseif head.level == toc_level then
if current_chapter then
local toc = current_chapter.toc
toc[#toc+1] = head
end
end
return nil
end

local function build_toc (heads)
local toc = {}
for _,head in ipairs(heads) do
local entry = {
pandoc.Plain{
pandoc.Link(
head.content:clone(), -- text
'#' .. head.identifier, -- target
"", -- empty title
pandoc.Attr(
"", -- empty identifier
{'local-toc-link'} -- class
)
)
}
}
toc[#toc+1] = entry
end
return pandoc.Div(
{ pandoc.BulletList(toc) },
pandoc.Attr( "", {'local-toc'} )
)
end


local function insert_toc (head)
if head.level == chapter_level then
local id = head.identifier
if headings[id] then
local toc = build_toc(
headings[id].toc
)
return {head,toc}
end
end
return nil
end

return {
{ Header = collect_headings },
{ Header = insert_toc },
}


On Friday, 31 January 2020 21:31:31 UTC+1, BP wrote:
>
> I believe a change has been made so that Lua filters now traverse the 
> document in linear order. If this is the case in the latest version of 
> Pandoc it should be doable with a two-pass filter: first a pass which 
> collects the headings and then a pass which inserts the TsoC. If you want 
> hierarchical section numbering you probably also need to do a first pandoc 
> run which inserts the numbering and then a second pandoc run with the 
> filter to insert the TsoC.  Something like this:
>
> (Warning 1: Untested code!
>   Warning 2: Make sure not to overwrite any existing file!
>   Warning 3: Assumes that all chapters are heading level 2 — change the 
> chapter_level and toc_level variables to match!
>    Warning 4: Assumes that each section/chapter has a unique identifier!
> )
>
> local chapter_level = 2
> local toc_level = 3
> local headings = {}
> local current_chapter = nil
>
> local function collect_headings (head)
>   if head.level == chapter_level then
>     local id = head.identifier
>     current_chapter = {
>       chapter = id
>       toc = {}
>     }
>     headings[id] = current_chapter
>   elseif head.level = toc_level then
>     if current_chapter then
>       local toc = current_chapter.toc
>       toc[#toc+1] = head
>     end
>   end
>   return nil
> end
>
> local function build_toc (heads)
>   local toc = {}
>   for _,head in ipairs(heads) do
>     local entry = {
>       pandoc.Plain{
>         pandoc.Link(
>           head.content:clone(), -- text
>           head.identifier, -- target
>           "", -- empty title
>           pandoc.Attr(
>             "", -- empty identifier
>             {'local-toc-link'} -- class
>           )
>         )
>       }
>     }
>     toc[#toc+1] = entry
>   end
>   return pandoc.Div(
>     { pandoc.BulletList(toc) },
>     pandoc.Attr( "", {'local-toc'} )
>   )
> end
>
>
> local function insert_toc (head)
>   if head.level = chapter_level then
>     local id = head.identifier
>     if headings[id] then
>       local toc = build_toc(
>         headings[id].toc
>       )
>       return {head,toc}
>     end
>   end
>   return nil
> end
>
> return {
>   { Header = collect_headings },
>   { Header = insert_toc },
> }
>
>
> Den fre 31 jan. 2020 19:27Szabolcs Horvát <szho...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org <javascript:>> 
> skrev:
>
>> Hello everyone,
>>
>> I am converting a Markdown file to HTML.
>>
>> I can insert a table of contents at the beginning using the --toc option.
>>
>> Is it possible to insert additional tables of contents under each 
>> level-two or level-three heading?
>>
>> I am looking to create something similar to the organization of this 
>> page: https://igraph.org/c/doc/igraph-Visitors.html#idm209455316208
>>
>> Szabolcs
>>
>> -- 
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>> email to pandoc-...-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org <javascript:>.
>> To view this discussion on the web visit 
>> https://groups.google.com/d/msgid/pandoc-discuss/3d838861-862c-4b15-8d91-a9b37d671736%40googlegroups.com 
>> <https://groups.google.com/d/msgid/pandoc-discuss/3d838861-862c-4b15-8d91-a9b37d671736%40googlegroups.com?utm_medium=email&utm_source=footer>
>> .
>>
>

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