copy

function copy(table1, table2, positionFunction)
    if not table1 then return end

    local table3 = table2 or {}

    positionFunction = positionFunction or function() return true end
    local position = 0

    for index, value in next, table1 do
        position = position + 1
        if (positionFunction and positionFunction(index, value, position)) then
            table3[index] = value
        end
    end

    return table3
end

------------------------------------------------------------------

local example = {[1]="a", [2]="b", [3]="c", [4]="d", [5]="e", [6]="f"}

local copied = copy(example, {}--[[, function(index, value, position)
    return position <= 4 --the result will be to copy only the first 4 things in "example" into an empty table
end]])


for i,v in next, copied do print(i,v) end --print out results