CSV to nested hashrequire 'csv'

nested_csv.rb

require 'csv'

users_by_id = {}
CSV.new(DATA, headers: true).each do |row|
  user_id = row['user_id'].to_i
  supervisor_id = row['supervisor_id'].to_i
  is_supervisor = row['is_supervisor'] == 't'
  existing_user = (users_by_id[user_id] ||= { user_name: row['user_name'], user_id: user_id})
  existing_user[:users] ||= [] if is_supervisor
  supervisor = users_by_id[supervisor_id]
  if supervisor
    supervisor[:users] << existing_user
  end
end

puts users_by_id[1].inspect


__END__
user_name,user_id,supervisor_id,is_supervisor
admin,1,0,t
foo,2,1,t
test,3,2,f

nested_csv_with_classes.rb

require 'csv'

class User
  attr_reader :name, :id

  def self.by_id
    @by_id ||= {}
  end

  def initialize(name, id)
    @name = name
    @id = id
    User.by_id[id] = self
  end

  def to_hash
    { :user_name => name, :user_id => id }
  end
end

class Supervisor < User
  attr_reader :users
  def initialize(name, id)
    super
    @users = []
  end

  def to_hash
    h = super
    h[:users] = users.map(&:to_hash)
    h
  end
end

root_user = nil
users_by_id = {}
CSV.new(DATA, headers: true).each do |row|
  user_id = row['user_id'].to_i
  supervisor_id = row['supervisor_id'].to_i
  is_supervisor = row['is_supervisor'] == 't'
  unless root_user
    root_user = Supervisor.new(row['user_name'], user_id)
  else
    user = if is_supervisor
      Supervisor.new(row['user_name'], user_id)
    else
      User.new(row['user_name'], user_id)
    end
    supervisor = User.by_id[supervisor_id]
    supervisor.users << user if supervisor
  end
end

puts root_user.to_hash


__END__
user_name,user_id,supervisor_id,is_supervisor
admin,1,0,t
foo,2,1,t
test,3,2,f

output.txt

$ ruby nested_csv.rb 
{:user_name=>"admin", :user_id=>1, :users=>[{:user_name=>"foo", :user_id=>2, :users=>[{:user_name=>"test", :user_id=>3}]}]}