Nested list value inside map csv export

The code is working fine it takes list of maps convert them into csv and export the value. This is the code

def to_csv(map, path) do
  file = File.open!(path, [:write, :utf8])
  map
   |> IO.inspect()
   |> CSV.encode(headers: true)
   |> Enum.each(&IO.write(file, &1))
end

This is the list of maps

%{
name: "Kelsie",    
date_of_birth: ~D[1944-06-02],
end_date: ~D[2017-10-30],   
category_id: [14, 9, 19, 14], 
room_name: "Filomena",
id: 11, 
},
%{ 
name: "Karson",
date_of_birth: ~D[1944-06-02],  
end_date: ~D[2017-11-04], 
category_id: [15, 19, 7, 14, 9],
room_name: "Bert",
id: 12,    
}
]

File is exporting successfully but the list of category ids not inserting . I just got \t\n in the place of category id.
Any suggestions?
If its possible?
Thanks