Cookbooks
Elixir
Chapter 10. Data Formats and Serialization
Working with CSV

Elixir:
Working with CSV

How to:

Elixir, with its powerful pattern matching and support for pipelining, can handle CSV files efficiently, even without third-party libraries. However, for more advanced needs, the nimble_csv library is a fast and straightforward choice.

Reading a CSV File Without External Libraries

You can read and parse a CSV file by using Elixir’s built-in functions:

defmodule CSVReader do
  def read_file(file_path) do
    File.stream!(file_path)
    |> Stream.map(&String.trim_trailing/1)
    |> Stream.map(&String.split(&1, ","))
    |> Enum.to_list()
  end
end

# Sample usage
CSVReader.read_file("data.csv")
# Output: [["Header1", "Header2"], ["Row1Value1", "Row1Value2"], ["Row2Value1", "Row2Value2"]]

Writing to a CSV File

Similarly, to write data to a CSV file:

defmodule CSVWriter do
  def write_to_file(file_path, data) do
    File.open(file_path, [:write], fn file ->
      Enum.each(data, fn row ->
        IO.write(file, Enum.join(row, ",") <> "\n")
      end)
    end)
  end
end

# Sample usage
data = [["Header1", "Header2"], ["Value1", "Value2"], ["Value3", "Value4"]]
CSVWriter.write_to_file("output.csv", data)
# Creates output.csv with the data formatted as CSV

Using nimble_csv

For more complex CSV handling, nimble_csv provides a powerful and flexible way to work with CSV data. First, add nimble_csv to your dependencies in mix.exs and run mix deps.get:

defp deps do
  [
    {:nimble_csv, "~> 1.2"}
  ]
end

Parsing CSV data with nimble_csv:

defmodule MyCSVParser do
  NimbleCSV.define(MyParser, separator: ",", escape: "\\")

  def parse(file_path) do
    file_path
    |> File.stream!()
    |> MyParser.parse_stream()
    |> Enum.to_list()
  end
end

# Sample usage
MyCSVParser.parse("data.csv")
# Output with nimble_csv can be customized based on the definition, but it generally looks like a list of lists or tuples depending on how you set up your parser.

Writing CSV data using nimble_csv requires manually transforming your data into a proper format and then writing it to a file, much like the plain Elixir example but leveraging nimble_csv for generating correctly formatted CSV rows.

By choosing the appropriate approach for your task’s complexity, you can handle CSV files in Elixir with great flexibility and power.

Working with JSON