task1.ex

defmodule CsvParser do
  def main([file | _args]) do
    {:ok, file_content} = File.read(file)
    parse(file_content)
  end

  def parse(content) when is_binary(content) do
    content
    |> String.split("\n")
    |> parse
  end

  def parse([_header | content]) do
    content
    |> Enum.map(&parse_line_raw/1)
    |> Enum.reduce(%{sum: 0, count: 0}, fn
      ([a,b,c], acc) when is_number(c) ->
        %{
          sum: acc.sum + c,
          count: acc.count+1
        }
      (_, acc) ->
        acc
    end)
  end

  def parse_line_raw(""), do: nil
  def parse_line_raw(line) do
    line
    |> String.split(",")
    |> Enum.map(&String.to_integer/1)
  end
end

# main stuff
System.argv()
|> CsvParser.main()
|> case do
  %{sum: sum, count: count} ->
    IO.puts "sum: #{sum}"
    IO.puts "mean: #{sum / count}"
end

############################################################################
# with stream (faster, less memory)

defmodule CsvParser do
  def main([file | _args]) do
    File.stream!(file)
    |> Enum.map(&parse_line_raw/1)
    |> Enum.reduce(%{sum: 0, count: 0}, fn
      ([a,b,c], acc) when is_number(c) ->
        %{
          sum: acc.sum + c,
          count: acc.count+1
        }
      (_, acc) ->
        acc
    end)
  end

  def parse_line_raw(line) do
    line
    |> String.split(",")
    |> Enum.map(&parse_col/1)
  end

  def parse_col(col) do
    Integer.parse(col)
    |> case do
      :error -> 0
      {i, _} -> i
    end
  end
end

# main stuff
System.argv()
|> CsvParser.main()
|> case do
  %{sum: sum, count: count} ->
    IO.puts "sum: #{sum}"
    IO.puts "mean: #{sum / count}"
end