sum.rb

array = [
  {
    cars: 4,
    houses: 5,
    job: {},
    fat: {},
  },
  {
    cars: 4,
    houses: 5,
    job: {},
    fat: {},
  },
  {
    cars: 4,
    houses: 5,
    job: {},
    fat: {},
  },
]



#array = array.reduce(Hash.new(0)) { |acc, h| acc.merge(h) { |_key, left, right| left + right } }
first, *rest = array
first.merge(*rest) { |key, left, right| left + right unless %i[job fat].include?(key) }.compact

p array

#=> [{:cars=>4, :houses=>5, :job=>{}, :fat=>{}}, {:cars=>4, :houses=>5, :job=>{}, :fat=>{}}, {:cars=>4, :houses=>5, :job=>{}, :fat=>{}}]