mix.exs

defmodule Stocks.Mixfile do
  use Mix.Project

  def project do
    [app: :stocks,
     version: "0.0.1",
     elixir: "~> 1.1",
     build_embedded: Mix.env == :prod,
     start_permanent: Mix.env == :prod,
     deps: deps]
  end

  def application do
    [applications: [:logger, :httpoison]]
  end

  defp deps do
    [
      {:httpoison, "~> 0.7.2"},
      {:csv, "~> 1.2.0"}
    ]
  end
end

stocks.exs

HTTPoison.start

defmodule StocksTest do
  def getClosingPrice(symbol, year) do
    resp = HTTPoison.get!("http://ichart.finance.yahoo.com/table.csv?s=#{symbol}&a=11&b=01&c=#{year}&d=11&e=31&f=#{year}&g=m")
    case resp.status_code do
      200 -> {:ok, {symbol, parseBody(resp.body)}}
      _   -> {:error, "Could not fetch the stock."}
    end
  end

  def parseBody(body) do
    body
    |> String.split("\n") # Convert the string into a Stream for the CSV library to parse.
    |> CSV.decode
    |> Enum.fetch!(1)
    |> Enum.fetch!(4)
    |> String.to_float
  end

  # Use the map/reduce idiom to remove any errors.
  def fetchMultiple(symbols, year) do
    Enum.map(symbols, &getClosingPrice(&1, year))
    |> Enum.reduce [], fn(f, acc) ->
      case f do
        {:ok, x} -> [x|acc]
        {:error, _} -> acc
      end
    end
  end

  def getHighestStock(symbols, year) do
    fetchMultiple(symbols, year)
    |> Enum.max_by fn({_, x}) -> x end # Use pattern matching on the tuple to grab the second (float) element.
  end
end

stocks = ['AAPL', 'GOOGL', 'IBM', 'ORCL', 'MSFT']
# Use pattern matching to grab the result out of the returned tuple.
{symbol, price} = StocksTest.getHighestStock(stocks, 2008)
IO.puts("The highest closing price was #{symbol} at $#{price}.")