Elixir function modifying a destination map only if a source map has a certain key whose value is processed and stored in the destination map.

play.ex

defmodule Play do
  def test1 do
    src = %{createdAt: "2017-01-19T08:32:26+02:00"}
    dest = %{}
    dest =
      case Map.has_key?(src, :createdAt) do
        true  ->
          {:ok, date, _} = DateTime.from_iso8601(src[:createdAt])
          Map.put(dest, :createdAt, date)
        false ->
          dest
      end
    dest
  end
end

Play.test1

Thanks @talentdeficit. Ended up slightly adapting a suggestion from Ben Wilson: https://www.irccloud.com/pastebin/mZJhLJLa/

EDIT: pasting in case the link stops working:

map = %{created_at: "2017-01-19T08:32:26+02:00", updated_at: "2017-01-19T08:32:26+02:00"}

converted = Map.new(map, fn
  {key, created_at} when key in [:created_at, :updated_at] ->
    {key, DateTime.from_iso8601!(created_at)}
  other ->
    other
end)