Inconsistent behavior of random for singleton RVs and draw sizes

[lucianopaz]

Description of your problem

This issue summarizes two inconsistent behaviors of pymc3's random method. One happens for distributions that are declared with shape (1,). The other happens when a distribution's random method is called with size=1.

Singleton array distributions

>>> import pymc3 as pm
>>> pm.Normal.dist(0, 1, shape=1).random().shape
()
>>> pm.Normal.dist(0, 1, shape=1).random(size=10).shape
(10,)

These two calls should output shapes (1,) and (10, 1) respectively. The singleton distribution dimension is incorrectly reduced.

Random draws of a single value

>>> import pymc3 as pm
>>> pm.Normal.dist(0, 1).random(size=1).shape
()
>>> pm.Normal.dist(0, 1, shape=1).random(size=1).shape
()
>>> pm.Normal.dist(0, 1, shape=10).random(size=1).shape
(10,)

These calls should output (1,), (1, 1) and (1, 10) respectively, but the single draw is incorrectly reduced. In particular, this behavior should only happen when we supply size=None or size=().

Versions and main components

• PyMC3 Version: 3.9.3
• Theano Version: 1.0.5
• Python Version: 3.7.6
• Operating system: Ubuntu
• How did you install PyMC3: (conda/pip) pip

[AlexAndorra]

@Sayam753, can we close this now that #4207 has been merged? Actually, can we close all the issues you mention in the PR's description?

[Sayam753]

Hi @AlexAndorra
This issue has been fixed by Michael is his #4214 PR. So, lets ping @michaelosthege to ask for closing this issue.
Coming to #4207, all the issues mention in the PR's description have been resolved. I think @twiecki closed them all.