根据多个键值来对数组排序

sort-by-multiple-keys.rb

def sort_by_multiple_keys(arr)
  
  # <=> operator to compare each element of the collection. 
  # This operator takes two arguments
  # returns
  # -1 if the first argument is less than the second argument
  #  1 if the second argument is less than the first argument
  #  0 if they're equivalent.
  
  # 1 <=> 2 # => -1  
  # 2 <=> 1 # => 1  
  # 1 <=> 1 # => 0 
  
  arr.sort { |a, b|
    [b[:key1], b[:key2], b[:key3]] <=> [a[:key1], a[:key2], a[:key3]]
  }
end