Re: Merging two lua tables

[BPJ via ntg-context <ntg-context@ntg.nl>]

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Hi,

I use the attached Lua function to merge array, map and mixed tables alike
(but differently! :-) The trick is to check if each key is numeric or not,
append if it is and overwrite if it isn't.

This function just ignores non-table arguments because that is what I
usually want. You may want to throw an error instead. Also it uses
table.pack. You might need to use `tab = {...}` and ipairs, or implement
pack:

``````lua
local function pack (...)
  return { n = select('#', ...), ... }
end
``````


Den mån 29 aug. 2022 14:32Aditya Mahajan via ntg-context <ntg-context@ntg.nl>
skrev:

> On Mon, 29 Aug 2022, Aditya Mahajan via ntg-context wrote:
>
> > Hi,
> >
> > How do I merge two lua tables? I believe that table.merge or
> table.merged should do the trick, but I cannot figure out how to use them.
> >
> > ```
> > local t1 = { 1, 2 }
> > local t2 = { 8, 9 }
> >
> > local m1 = {}
> > table.merge(m1,t1, t2)
> > table.print(m1)
> >
> > local m2 = table.merged(t1, t2)
> > table.print(m2)
> > ```
> >
> > Processing the file with context filename shows that both m1 and m2 are
> {8, 9}. What am I missing.
>
> Looking at the code, I see what is happening. table.merge(d) assume that
> the tables are key-value tables so the keys of the first table are silently
> overwritten by the send. I guess, I'll have to write my own function to
> merge "array" tables.
>
> Aditya
>
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local function merge_tables (...)
  tab = table.pack(...)
  rv  = {}
  for i=1,tab.n do
    -- Is it a table? Ignore if not!
    if 'table' == type(tab[i]) then
      for k,v in pairs(tab[i]) do
        -- Is the key a number?
        if 'number' == type(k) then
          -- Append it!
          rv[#rv+1] = v
        else
          -- Non-numeric key: overwrite value
          rv[k] = v
        end
      end
    end
  end
  return rv
end

dump = require"pl.pretty".dump

tab_a = {
  'a', 'b', 'c',
  foo = 'A',
  bar = 'B',
  baz = 'C',
}

tab_b = {
  'd', 'e', 'f',
  baz = 'D',
  bop = 'E',
  fop = 'F',
}

merged = merge_tables(tab_a, 'quux', tab_b, 0.0)

dump(merged)
  

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