Get position from one list and choose element of another list in Compile

Question

How can do it?

t = {};
f = 
 Compile[{{l, _Integer}}, 
   Module[
     {list = {{1, 1, 1}, {2, 2, 2}, {3, 3, 3}}}, 
     Map[AppendTo[t, list[[#]] &], l]]; 
     t
   ];

CompiledFunction::cfta

there is two related question: this and this.

Update: with help of Sumit (here) I write another function but still there is problem with Sequence@@.

Compile[{{l, _Integer}}, 
  Module[{positions = {1, 2, 4}},
   Table[KroneckerDelta[#1, 
       Sequence @@ Flatten@Position[list, #2]]*#2 &[x, y], 
      {x,positions}, {y, l}]
   ]
]

Or this:

  f = Compile[{{r, _Integer, 2}},
  Table[
    Map[KroneckerDelta[p, Position[r, #][[1]]]*# &, r], {p, {2, 4}}]]

Answer 1

You are using the global symbol t within a compiled function. This is not going to work like you expect it. What you probably want is the following simple function providing that I understood you correctly:

f = Compile[{{l, _Integer, 1}}, Module[{
     list = {{1, 1, 1}, {2, 2, 2}, {3, 3, 3}},
     t = Most[{{1}}]},
    t = Map[list[[#]] &, l];
    t
  ]
];

No AppendTo needed and it gives you a local t that you can use inside the compiled function itself.

f[{1, 2, 1, 3}]
(* {{1, 1, 1}, {2, 2, 2}, {1, 1, 1}, {3, 3, 3}} *)

Please pay attention that you have to help Compile determining the correct data types. I explicitly defined l as a list of numbers and even the expression

Most[{{1}}]

only gives the empty list {}, BUT the compiler saw that I had a list of integer lists and therefore, assumes t should have exactly this type.