a,b
1,2
3,4
...

{a: 1, b: 2} #1
{a: 3, b: 4} #2
...

def map_stream(enum) do
    enum
    |> Stream.transform(:first, &structure_from_header/2)
    |> Stream.drop(1)
end

#The accumulator starts as :first, the its the structure of the csv
#that is the first line
def structure_from_header(line, :first),
    do: { [ nil ], line }

def structure_from_header(line, structure) do
    map =
      structure
      |> Enum.zip(line)
      |> Enum.into(%{})

{ [ map ], structure }
end