Imagestack.sel is very slow on large volumes

[ambrosejcarr]

My understanding is that ImageStack.sel should produce a view of the data in ImageStack. However, attempts to select data from a large volume takes a very long time (~5-10 seconds), which makes me wonder if it is copying.

Reproduce:

import starfish.data
from starfish.types import Axes
image = starfish.data.SeqFISH(use_test_data=False).fov().get_image('primary')
round_1 = image.sel({Axes.ROUND: 1})

Desired outcome: Selection from ImageStack is fast (< 1s).

[ttung]

sel is doing a copy, apparently. That is not great.

[ambrosejcarr]

This may be an edge case -- I'm loading a 33 GB volume into memory, and selecting rounds from it because I couldn't use our select-on-load capabilities. I will be able to avoid this particular situation in the future.