Ruby mongoDB map reduce

mongodb_map_reduce.rb

# Ruby mongoDB map reduce 
# The mongoDB documentation missed totally to 
#  describes a simple usage for map reduce in Ruby.
# and the web is full of misleading example based on the previous API.
#
# This gist try to fill out the gap.
# First please read https://docs.mongodb.org/manual/tutorial/map-reduce-examples/
#  below it is a simple Ruby implementation.
#
# @doc     https://docs.mongodb.org/manual/core/map-reduce/
# @example https://docs.mongodb.org/manual/tutorial/map-reduce-examples/
# @date    20 March 2016
# @author  vikoky
#
# Tools
# ---
# Ruby 2.2.1 
# MongoDB drive 2.2.0
# Mongo 2.6 
#

mapFunc = %q(
      var mapFunction1 = function() {
        emit(this.product_id, {price: this.price});
    };
)

reduceFunc = %q(
      var reduceFunction1 = function(keyCustId, values)
      {
        var a = values[0]; // will reduce into here
        for (var i=1; i < values.length; i++)
        {
             var b = values[i];
             a.price += b.price;
        }
        return a;
       };
)

# Connect to mongoDB
db = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'example')
db[:product].insert_one( { product_id: 0, price: 20 } )
db[:product].insert_one( { product_id: 0, price: 30 } )
db[:product].insert_one( { product_id: 1, price: 10 } ) 

# Prepare Map Reduce
mr = db[:product].find().map_reduce(mapFunc, reduceFunc)
mr.out(inline: 1)
mr.verbose(true)
    
# Execute/Display results
p mr.to_a
# or
mr.each do |doc|
  p doc
end