Working with CSV

How to:

Ruby includes the CSV library by default, which simplifies reading from and writing to CSV files. Here’s how you can leverage this for common tasks:

Reading a CSV file

To read from a CSV file, you first require the CSV library. Then, you can iterate over rows or read them into an array.

require 'csv'

# Reading each row as an array
CSV.foreach("data.csv") do |row|
  puts row.inspect

# Output for each row might look like this: ["data1", "data2", "data3"]

Writing to a CSV

Writing to a CSV file is also straightforward. You can append to an existing file or create a new file to write.

require 'csv'"output.csv", "wb") do |csv|
  csv << ["header1", "header2", "header3"]
  csv << ["value1", "value2", "value3"]

# This creates or overwrites 'output.csv' with the specified headers and values.

Parsing a CSV string

Sometimes you need to parse CSV data directly from a string. Here’s how:

require 'csv'

data = "name,age,city\nJohn Doe,29,New York\nJane Doe,31,Chicago"
csv = CSV.parse(data, headers: true)

csv.each do |row|
  puts "#{row['name']} - #{row['age']} - #{row['city']}"

# Expected output:
# John Doe - 29 - New York
# Jane Doe - 31 - Chicago

Using SmarterCSV

For more complex CSV tasks, the SmarterCSV gem can be a valuable tool. First, install the gem:

gem install smarter_csv

Then, you can use it to deal with large files or perform more sophisticated parsing and manipulation:

require 'smarter_csv'

options = {}
data = SmarterCSV.process('large_data.csv', options)

data.each do |hash|
  puts hash.inspect

# This will read 'large_data.csv' and output each row as a hash based on the headers.

To sum up, Ruby’s built-in CSV library, along with third-party gems like SmarterCSV, provides robust support for handling CSV data, allowing for efficient data processing and manipulation tasks.