Lua : remove duplicate elements

Question

i am having a table in lua

test = {1,2,4,2,3,4,2,3,4,"A", "B", "A"}

I want to remove all duplicate elements in table.
Output should be

test = {1,2,4,3,"A","B"}

EDIT:

My try :

> items = {1,2,4,2,3,4,2,3,4,"A", "B", "A"}
> flags = {}
> for i=1,table.getn(items)  do
if not flags[items[i]] then
      io.write(' ' .. items[i])
      flags[items[i]] = true
   end
>> end
 1 2 4 3 A B>

It is working fine now. Thanks for answers and comments.

Answer 1

Similar to example given by @Dimitry but only one loop

local test = {1,2,4,2,3,4,2,3,4,"A", "B", "A"}
local hash = {}
local res = {}

for _,v in ipairs(test) do
   if (not hash[v]) then
       res[#res+1] = v -- you could print here instead of saving to result table if you wanted
       hash[v] = true
   end

end

Answer 2

local test = {1,2,4,2,3,4,2,3,4,"A", "B", "A"}

-- make unique keys
local hash = {}
for _,v in ipairs(test) do
    hash[v] = true
end

-- transform keys back into values
local res = {}
for k,_ in pairs(hash) do
    res[#res+1] = k
end

-- 1 2 3 4 A B
for _,v in ipairs(res) do
    print(v)
end

test = res

... a simple, straightforward solution just from the head, but I think, the hint is given in the PiL book

what have you tried to solve the problem?

Answer 3

local xx = {'a','b','c','d','a','d','f','g','a'}
table.sort(xx)
local result = {}

for key,value in ipairs(xx) do
  if value ~=xx[key+1] then
    table.insert(result,value)
  end
end

for key,value in ipairs(result) do
  print(key,value)   
end