gistfile1.rb

#sebcioz: programs is a hash containing rows from a mysql query with two fields: program_id and program_name.
#participants is a hash containing rows from a mysql query with several fields, one of which is program_id. I would like to create a third hash that puts participants into groups based on program_id

programs = [{:program_id => 1, :program_name => :a}, {:program_id => 2, :program_name => :b}, {:program_id => 3, :program_name => :c}]
participants = [{:name => :q, :program_id => 1}, {:name => :w, :program_id => 1}, {:name => :e, :program_id => 2}]

groups = participants.group_by { |p| p[:program_id] }

p groups #=> {1=>[{:name=>:q, :program_id=>1}, {:name=>:w, :program_id=>1}], 2=>[{:name=>:e, :program_id=>2}]}