merge two tables in lua

merge-table.lua

function table.merge(t1, t2)
   for k,v in ipairs(t2) do
      table.insert(t1, v)
   end 
 
   return t1
end

If anyone else is running into this and it doesn't work, note that it only works for lists ("arrays"), not associative arrays. Here's a version for associative arrays:

-- For associative arrays
function object_assign(t1, t2)
	for key, value in pairs(t2) do
	   t1[key] = value
	end 

	return t1
end

-- object_assign({ name = "Miles Davis" }, { genre = "Jazz" })
--> { name = "Miles Davis", genre = "Jazz" } 

I modify merge table fucntion, very useful~~

for example:
talbe a:
{
[1] = 1,
[2] = 2,
[3] = 3,
[4] = 4,
[5] = 5,
[6] = 6,
[7] = 7,
[8] = 8,
[9] = 9
}
table b:
{
["d"] = 4,
["e"] = {
["z"] = 3,
["x"] = 1,
["y"] = 2
},
[2] = "y",
["a"] = 1,
["b"] = 2,
[1] = "x",
["c"] = 3
}
merge results table:
{
[1] = 1,
[2] = 2,
[3] = 3,
[4] = 4,
[5] = 5,
[6] = 6,
[7] = 7,
[8] = 8,
[9] = 9,
[10] = "y",
[11] = "x",
["d"] = 4,
["e"] = {
["z"] = 3,
["x"] = 1,
["y"] = 2
},
["a"] = 1,
["b"] = 2,
["c"] = 3
}

so cool!, list append, dict add node!

--source:
local function table_merge(...)
    local tables_to_merge = { ... }
    assert(#tables_to_merge > 1, "There should be at least two tables to merge them")

    for k, t in ipairs(tables_to_merge) do
        assert(type(t) == "table", string.format("Expected a table as function parameter %d", k))
    end

    local result = table_clone(tables_to_merge[1])

    for i = 2, #tables_to_merge do
        local from = tables_to_merge[i]
        for k, v in pairs(from) do
            if type(v) == "table" then
                result[k] = result[k] or {}
                assert(type(result[k]) == "table", string.format("Expected a table: '%s'", k))
                result[k] = table_merge(result[k], v)
            elseif type(k) == "string" then
                result[k] = v
            else
                table.insert(result, v)
            end
        end
    end

    return result
end

TLDR; I understand @dmitrii-eremin that you code helps to clone the contents, but if you can list/highlight the problem in the original answer it will help...

@LRagji Sorry for such a late reply :-)

• The original code goes only though indexed arrays, not through all table elements.
• The original code does not clone objects, it just saves a reference to object to other place. So if the original object is changed, then the cloned is changed as well.

I write a better one! injoin it!

function table_merge(...)
    local tables_to_merge = { ... }
    assert(#tables_to_merge > 1, "There should be at least two tables to merge them")

    for k, t in ipairs(tables_to_merge) do
        assert(type(t) == "table", string.format("Expected a table as function parameter %d", k))
    end

    local result = tables_to_merge[1]

    for i = 2, #tables_to_merge do
        local from = tables_to_merge[i]
        for k, v in pairs(from) do
            if type(k) == "number" then
                table.insert(result, v)
            elseif type(k) == "string" then
                if type(v) == "table" then
                    result[k] = result[k] or {}
                    result[k] = table_merge(result[k], v)
                else
                    result[k] = v
                end
            end
        end
    end

    return result
end

function merge_table(table1, table2)
	for _, value in ipairs(table2) do
		table1[#table1+1] = value
	end
	return table1
end

-- example
local table1 = {1, 2, 3}
local table2 = {4, 5, 6}

merged_table = merge_table(table1, table2)
for _, value in ipairs(merged_table) do
	print(value)
end

output
------------------
1
2
3
4
5
6