Create a CSV file from an array of hashes

csv_play.rb

require 'csv'

# This is the source data - basically an array of hashes
data = [
  {a: 1, b: 2},
  {a: 3, b: 4}
]

# This is a path to the file we are going to create.
# __dir__ is the directory of the current file - that is, this file's directory
# So this will create a path to a file 'csv_play.csv' in the same directory as this file
# The file doesn't need to exist - the next line will create it
path = File.join __dir__, 'csv_play.csv'

# This line opens the new file and the following lines write the data to it
CSV.open(path, 'wb') do |csv|

  # The first line of the CSV needs to be the headers. That's the keys
  # of the hashes. If we assume all the hashes have the same keys we can
  # just pick the first one and use it's keys to create the first line
  csv << data.first.keys

  # Then we just iterate through the hashes, pushing the values of each
  # into the csv.
  data.each do |row|
    csv << row.values
  end
end

# If you run this file `ruby csv_play.rb`, a file will be created in the same directory
# The file will have the content:
#
#   a,b
#   1,2
#   3,4