Applying custom base conditions to frequency views

[jamesrkg]

We need a way to apply conditions onto the implied base of frequency views so as to allow for fine control over proportional (%) results.

In effect, this is cusomization of the kwarg rel_to:

'rel_to': [
    None, 
    'y', 
    {'y': {'x': has_any(frange('1-8'))}}
]

In this case, three sets of views are created - counts, natural-c% and custom-c% using the additional logical condition {'x': has_any(frange('1-8'))}.

Custom rel_to instructions follow the convention {axis_of_orientation: wildcard_logical_condition} where wildcard_logical_condition can be any wildard custom logic with the added option of using the shorthand keys x or y to refer to the given link's x or y variables. This shorthand would only be available for non-nested link axes!

The view keys, respectively, would be (I'm using the view key notation proposed in #67):

rel_to: None --> x|f|:|||my_net
rel_to: 'y' --> x|f|:|y||my_net
rel_to: {'y': {'x': has_any(frange('1-8'))}} --> x|f|:|y:x[{1,2,3,4,5,6,7,8}]||my_net

[alextanski]

I think we must turn the base def. into a part of a block net defintion to make this more flexible and easier to manage. If we modify the rel_to parameter using the logics, this would mean that we generate one version that is basing on all, then one basing on the logical index length. The block net however will never be correct as a whole.

This implies slicing and concat. views when chaining stuff for exports, a thought that gives me pain in every part of my body.

[alextanski]

Also: what we really need is a "rebaser" method that returns an array of column bases depending on a condition.