def describe
      Daru::Vector.new(
        size: size,
        categories: categories.size,
        max_freq: @cat_hash.values.map(&:size).max,
        max_category: @cat_hash.keys.max_by { |cat| @cat_hash[cat].size },
        min_freq: @cat_hash.values.map(&:size).min,
        min_category: @cat_hash.keys.min_by { |cat| @cat_hash[cat].size }
      )
    end
Gives the summary of data using following parameters
- size: size of the data
- categories: total number of categories
- max_freq: Max no of times a category occurs
- max_category: The category which occurs max no of times
- min_freq: Min no of times a category occurs
- min_category: The category which occurs min no of times
@return [Daru::Vector] Vector with index as following parameters
and values as values to these parameters
@example
dv = Daru::Vector.new [:a, 1, :a, 1, :c], type: :category
dv.describe
# => #<Daru::Vector(6)>
#         size            5
#   categories            3
#     max_freq            2
# max_category            a
#     min_freq            1
# min_category            c