Hi,

this is a very special form of "merging", so I don't think there's a 
built-in method for this.

But you can use the block form of Hash#merge:

#-------------------------------------
foo = {"luxuy" => ["Mercedes", "BMW"], "sport" => ["Ferrari"]}
bar = {"luxuy" => ["BMW", "Bentley"], "sport"=>["Lamborghini"]}

merg = foo.merge bar do |_, arr_1, arr_2|
  arr_1 + arr_2
end
p merg
#-------------------------------------

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