Lua - Merging Arrays

We can append two arrays or tables together in Lua with a trivial function, but it should be noted that no library function exists for the same.

There are different approaches to concatenating two tables in Lua. We've two approaches that can perform more or less the same when it comes to complexity.

The first approach looks something like this −

function tableConcat(t1,t2)
   for i=1,#t2 do
      t1[#t1+1] = t2[i]
   end
   return t1
end

Another approach of achieving the same is to make use of the ipairs() function.

Example

Consider the example shown below −

for _,v in ipairs(t2) do
   table.insert(t1, v)
end

We can use either of these approaches. Now let's use the first one in a Lua example.

Example - Merging Arrays

Consider the example shown below −

main.lua

-- initialize two arrays
t1 = {1,2}
t2 = {3,4}

-- concatenate the tables
function tableConcat(t1,t2)
   -- loop over t2 items
   for i=1,#t2 do
      -- append entries to t1   
      t1[#t1+1] = t2[i]
   end
   -- return merged table
   return t1
end

-- call the function to concatenate arrays
t = tableConcat(t1,t2)

-- print the merged values
for _, v in pairs(t1) do 
   print(v) 
end

Output

When we run the above program, we will get the following output −

1
2
3
4

Example - Merging Arrays using ipairs()

Consider the example shown below −

main.lua

-- initialize two arrays
t1 = {1,2}
t2 = {3,4}

-- concatenate the tables
function tableConcat(t1,t2)
   -- loop over t2 items   
   for _,v in ipairs(t2) do
      -- append entries to t1   
      table.insert(t1, v)
   end
   -- return merged table
   return t1
end

-- call the function to concatenate arrays
t = tableConcat(t1,t2)

-- print the merged values
for _, v in pairs(t1) do 
   print(v) 
end

Output

When we run the above program, we will get the following output −

1
2
3
4