Merging two lua tables

Merging two lua tables

[Aditya Mahajan via ntg-context]

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. 

Thanks,
Aditya
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Re: Merging two lua tables

[Aditya Mahajan via ntg-context]

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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Re: Merging two lua tables

[BPJ via ntg-context]

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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
>
> ___________________________________________________________________________________
> If your question is of interest to others as well, please add an entry to
> the Wiki!
>
> maillist : ntg-context@ntg.nl /
> https://www.ntg.nl/mailman/listinfo/ntg-context
> webpage  : https://www.pragma-ade.nl / http://context.aanhet.net
> archive  : https://bitbucket.org/phg/context-mirror/commits/
> wiki     : https://contextgarden.net
>
> ___________________________________________________________________________________
>

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[-- Attachment #2: table-merge.lua --]
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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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Re: Merging two lua tables

[Hans Hagen via ntg-context]

On 8/29/2022 7:33 PM, BPJ via ntg-context wrote:
> 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.

you really want something like this then:

local  tab = table.pack(...)
local  rv  = {}

> 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:
I might add table.himerged (hash and index) but slightly different (and 
some 30% faster) to util-tab but i think merging mixed hash/indexed 
tables is rare.

Hans

-----------------------------------------------------------------
                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------
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___________________________________________________________________________________

Re: Merging two lua tables

[BPJ via ntg-context]

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Den mån 29 aug. 2022 20:13Hans Hagen via ntg-context <ntg-context@ntg.nl>
skrev:

> On 8/29/2022 7:33 PM, BPJ via ntg-context wrote:
> > 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.
>
> you really want something like this then:
>
> local  tab = table.pack(...)
> local  rv  = {}
>

Thanks. I was manually translating from MoonScript (https://moonscript.org)
where variables are local by default.


> > 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:
> I might add table.himerged (hash and index) but slightly different (and
> some 30% faster) to util-tab but i think merging mixed hash/indexed
> tables is rare.
>
> Hans
>
> -----------------------------------------------------------------
>                                            Hans Hagen | PRAGMA ADE
>                Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
>         tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
> -----------------------------------------------------------------
>
> ___________________________________________________________________________________
> If your question is of interest to others as well, please add an entry to
> the Wiki!
>
> maillist : ntg-context@ntg.nl /
> https://www.ntg.nl/mailman/listinfo/ntg-context
> webpage  : https://www.pragma-ade.nl / http://context.aanhet.net
> archive  : https://bitbucket.org/phg/context-mirror/commits/
> wiki     : https://contextgarden.net
>
> ___________________________________________________________________________________
>

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___________________________________________________________________________________

Re: Merging two lua tables

[BPJ via ntg-context]

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Come to think of it you may also want to check that numeric indices are
indeed positive integers before appending their value. I usually don't
because their not being so is rare.

Den tis 30 aug. 2022 10:56BPJ <bpj@melroch.se> skrev:

>
>
> Den mån 29 aug. 2022 20:13Hans Hagen via ntg-context <ntg-context@ntg.nl>
> skrev:
>
>> On 8/29/2022 7:33 PM, BPJ via ntg-context wrote:
>> > 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.
>>
>> you really want something like this then:
>>
>> local  tab = table.pack(...)
>> local  rv  = {}
>>
>
> Thanks. I was manually translating from MoonScript (https://moonscript.org)
> where variables are local by default.
>
>
>> > 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:
>> I might add table.himerged (hash and index) but slightly different (and
>> some 30% faster) to util-tab but i think merging mixed hash/indexed
>> tables is rare.
>>
>> Hans
>>
>> -----------------------------------------------------------------
>>                                            Hans Hagen | PRAGMA ADE
>>                Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
>>         tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
>> -----------------------------------------------------------------
>>
>> ___________________________________________________________________________________
>> If your question is of interest to others as well, please add an entry to
>> the Wiki!
>>
>> maillist : ntg-context@ntg.nl /
>> https://www.ntg.nl/mailman/listinfo/ntg-context
>> webpage  : https://www.pragma-ade.nl / http://context.aanhet.net
>> archive  : https://bitbucket.org/phg/context-mirror/commits/
>> wiki     : https://contextgarden.net
>>
>> ___________________________________________________________________________________
>>
>

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___________________________________________________________________________________
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maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context
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___________________________________________________________________________________

Re: Merging two lua tables

[Hans Hagen via ntg-context]

On 8/29/2022 2:20 PM, 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.
table.imerge(m1,t1, t2)

-----------------------------------------------------------------
                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------
___________________________________________________________________________________
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___________________________________________________________________________________

Re: Merging two lua tables

[Aditya Mahajan via ntg-context]

On Mon, 29 Aug 2022, Hans Hagen via ntg-context wrote:

> On 8/29/2022 2:20 PM, 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.
> table.imerge(m1,t1, t2)

Ah, thanks!

Aditya
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