Filtering on the group variable causes some unexpected behavior

[jwildfire]

Difference column is drawn with no content.

  const settings = {
        'variables': {
            'group': 'ARM',
            'filters': [ { 'value_col': 'ARM', 'label': 'Arm','type': 'participant' }: start:["Placebo"]}
        };

[jwildfire]

Not sure what expected behavior is here. I guess we could:

1. interactively suppress the columns for Arms when they are filtered
2. not allow filters for group variables
3. something else i'm not thinking of ...

@pburnsdata @samussiah @emmorris @rtbailey - Thoughts?

[pburnsdata]

I don't mind option 1. So the column for an arm would only display when that arm is in the filter and the difference column would only appear when at least two are selected?