map

 # I need to turn
  
 [ {:class_fk => 1234, :criteria => "citizenship", :grade => "A"},
   {:class_fk => 1234, :criteria => "effort", :grade => "B"} ]
 
 # into 
 
 { 1234 => {"citizenship" => "A", "effort" => "B"} }
 
 
 # I have this
 
 @citizenship_effort = @citizenship_effort.map {|v| {class_pk: v[:class_pk], v[:criteria] => v[:grade]}}.group_by {|x| x[:class_pk]}
 
 # but it results in 
 
 {1234=>[{:class_pk=>1234, "citizenship"=>"A"}, {:class_pk=>1234, "Effort"=>"B"}] }