DummyReader should be convertable to a MemoryReader

[kain88-de]

Is your feature request related to a problem? Please describe.

I would like to create a dummy universe with a trajectory attached. I can create the dummy universe. I do not know how I load a numpy array as a trajectory into it.

This would work nicely as a feature with our new trajectory writer shortcut.

Describe the solution you'd like

u = mda.Universe.empty(2, trajectory=True)
# shape is (n_frames, n_atoms, 3)
u.trajectory.add_coordinates(np.ones((100, 2, 3))

Describe alternatives you've considered
I could load a file from the test trajectories.

[orbeckst]

Can you do a u.transfer_to_memory()?

[kain88-de]

If iteration won't work then `transfer_to_memory` won't work either. It iterates over a trajectory.

…

On Tue, Sep 18, 2018 at 7:17 PM Oliver Beckstein ***@***.***> wrote: Can you do a u.transfer_to_memory()? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#2077 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AEGnVtgztuvVnWQzSZOWQr7R0ar70Hvsks5ucSqPgaJpZM4Wt3JZ> .

[richardjgowers]

Related to #2076 we should just nuke dummyreader and replace with memory