How to expand/reduce a two-dimensional Ruby NArray?

Question

If I have a Narray with the shape 100, 10000 and want to expand it to say 100, 20000 (basically add rows) what is the proper way to achieve this? To expand massive Narrays I would like to avoid using a temporary Narray for memory reasons.

Answer 1

require "narray"

class NArray
  def expand(*new_shape)
    na = NArray.new(self.typecode,*new_shape)
    range = self.shape.map{|n| 0...n}
    na[*range] = self
    return na
  end
end

p a = NArray.float(2,3).indgen!
# => NArray.float(2,3):
#    [ [ 0.0, 1.0 ],
#      [ 2.0, 3.0 ],
#      [ 4.0, 5.0 ] ]

p a.expand(3,4)
# => NArray.float(3,4):
#    [ [ 0.0, 1.0, 0.0 ],
#      [ 2.0, 3.0, 0.0 ],
#      [ 4.0, 5.0, 0.0 ],
#      [ 0.0, 0.0, 0.0 ] ]

There is no general way to expand a memory block without movement. Memory block can be extended only if enough free area follows, but such a case is usually unexpected.