Convert JSON file to CSV

json2csv.rb

require 'csv'
require 'json'

# parse some json into hash array
data = JSON.parse(File.read("in.json"))

# get all headers appearing anywhere in data
keys = []
data.each do |hash|
  keys = keys.concat(hash.keys).uniq
end

f = File.open "out.csv", "w"

f << CSV.generate do |csv|
  csv << keys # write headers
  data.each do |hash|
    # make a new hash, which sets any missing key values to nil
    h2 = {}
    keys.each do |k|
      h2[k] = hash[k]
    end
    csv << h2.values # write those values to csv
  end
end
f.close