def replace_values old_values, new_value
      @data.each { |vec| vec.replace_values old_values, new_value }
      self
    end
Replace specified values with given value
@param [Array] old_values values to replace with new value
@param [object] new_value new value to replace with
@return [Daru::DataFrame] Data Frame itself with old values replace
with new value
@example
df = Daru::DataFrame.new({
a: [1,    2,          3,   nil,        Float::NAN, nil, 1,   7],
b: [:a,  :b,          nil, Float::NAN, nil,        3,   5,   8],
c: ['a',  Float::NAN, 3,   4,          3,          5,   nil, 7]
}, index: 11..18)
df.replace_values nil, Float::NAN
# => #<Daru::DataFrame(8x3)>
#       a   b   c
#   11   1   a   a
#   12   2   b NaN
#   13   3 NaN   3
#   14 NaN NaN   4
#   15 NaN NaN   3
#   16 NaN   3   5
#   17   1   5 NaN
#   18   7   8   7