Cloning Tables

5 min

Sometimes it’s useful to be able to copy or “clone” a table. Lua provides no built-in function to copy tables, but the following methods can help.

Shallow Copies

A “shallow copy” is useful for copying a table that’s one level deep — meaning, a basic array or dictionary table without any nested tables inside it.

Dictionaries

A dictionary table can be shallow copied by looping over the original table’s keys using pairs and assigning them to another table:

				
					Expected Output
				
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			local function shallowCopy(original)
	local copy = {}
	for key, value in pairs(original) do
		copy[key] = value
	end
	return copy
end
		
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In practice, the copy can be made as follows:

				
					Expected Output
				
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			local original = {
	key = "value",
	engine = "Roblox",
	playerID = 505306092
}
local clone = shallowCopy(original)

for key, value in pairs(clone) do
	print(key, value)
end
		
			playerID 505306092
key value
engine Roblox
		
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Arrays

For arrays, the Lua unpack() function can do most of the work:

				
					Expected Output
				
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			local original = {1, 3, 5, 7, 9}
local clone = {unpack(original)}

for i = 1, #clone do
	print(clone[i])
end
		
			1
3
5
7
9
		
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In Roblox, this only works for arrays up to 7999 items due to tuple behavior.

Deep Copies

Sometimes a shallow copy isn’t enough. Tables with nested tables inside it must be copied with a recursive function:

				
					Expected Output
				
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			local function deepCopy(original)
	local copy = {}
	for k, v in pairs(original) do
		if type(v) == "table" then
			v = deepCopy(v)
		end
		copy[k] = v
	end
	return copy
end
		
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With the function in place, a deep copy can be made as follows:

				
					Expected Output
				
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			local original = {
	key = "value",
	playerInfo = {
		playerID = 505306092,
		playerName = "IgnisRBX"
	},
	otherInfo = {
		{
			{1, 3, 5, 7, 9}
		}
	}
}
local clone = deepCopy(original)

print(clone["playerInfo"]["playerID"])
print(clone["otherInfo"][1][1][4])
		
			505306092
7
		
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Tags:

cloning
tables

Cloning Tables

Cloning Tables

Shallow Copies

Dictionaries

Arrays

Deep Copies

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