def count_values(*values)
      values.map { |v| @cat_hash[v].size if @cat_hash.include? v }
            .compact
            .inject(0, :+)
    end
def count_values(*values)
      values.map { |v| @cat_hash[v].size if @cat_hash.include? v }
            .compact
            .inject(0, :+)
    end
Count the number of values specified
 @param [Array] values to count for
 @return [Integer] the number of times the values mentioned occurs
 @example
   dv = Daru::Vector.new [1, 2, 1, 2, 3, 4, nil, nil]
   dv.count_values nil
   # => 2