gistfile1.rb

 > elements = {a1: 'a', b1: 'b', b2: 'b', b3: 'b', c1: 'c'}
 => {:a1=>"a", :b1=>"b", :b2=>"b", :b3=>"b", :c1=>"c"}
 > elements.group_by {|(_, val)| val }.flat_map {|(_, vals)| vals.shuffle }
 => [[:a1, "a"], [:b2, "b"], [:b3, "b"], [:b1, "b"], [:c1, "c"]] 
 > elements.group_by {|(_, val)| val }.flat_map {|(_, vals)| vals.shuffle }
 => [[:a1, "a"], [:b1, "b"], [:b3, "b"], [:b2, "b"], [:c1, "c"]] 
 > elements.group_by {|(_, val)| val }.flat_map {|(_, vals)| vals.shuffle }
 => [[:a1, "a"], [:b1, "b"], [:b3, "b"], [:b2, "b"], [:c1, "c"]] 
 > elements.group_by {|(_, val)| val }.flat_map {|(_, vals)| vals.shuffle }
 => [[:a1, "a"], [:b2, "b"], [:b1, "b"], [:b3, "b"], [:c1, "c"]] 
 > elements.group_by {|(_, val)| val }.flat_map {|(_, vals)| vals.shuffle }
 => [[:a1, "a"], [:b3, "b"], [:b2, "b"], [:b1, "b"], [:c1, "c"]]