def min(size=nil, &block)
            reject_values(*Daru::MISSING_VALUES).to_a.min(size, &block)
          end
Returns the minimum value(s) present in the vector, with an optional comparator block.

@param size [Integer] Number of minimum values to return. Defaults to nil.

@example

dv = Daru::Vector.new (["Tyrion", "Daenerys", "Jon Starkgaryen"]), index: Daru::Index.new([:t, :d, :j])
#=>
#   #<Daru::Vector(3)>
#       t   Tyrion
#       d   Daenerys
#       j   Jon Starkgaryen

dv.min
#=> "Daenerys"

dv.min(2) { |a,b| a.size <=> b.size }
#=> ["Tyrion","Daenerys"]