With elixir you don’t (and usually can’t) solve issues by using loops like you’d do in non-functional languages. You’d want to look into reducing over your data to get to the expected result. for might look like a loop, but it’s not.

You should try not to think how You would solve this in your previous language. It will only slow You down.

A good start, as mentionned by @al2o3cr is to learn the Enum module.

A solution with Enum.reduce might look like this. What You need to understand, value don’t change, but can be transformed.

{list, previous, count} = Enum.reduce(list_of_integer, {[], nil, 0}, fn integer, {list, previous, count} -> 
  if integer == previous do
    ... return an acc with incremented count
  else
   ... return an acc with count = 1, previous = integer, update list with new element
  end
end)

Could use Enum.reduce/3!

reducer = fn (digit, acc) ->
  case acc[digit] do
    nil -> Map.put(acc, digit, 1)
    current_count -> Map.put(acc, digit, current_count + 1)
  end
end

11223411
|> Integer.to_string
|> String.graphemes
|> Enum.reduce(%{}, reducer)
|> Map.to_list

Result: [{"1", 4}, {"2", 2}, {"3", 1}, {"4", 1}]