I'm using:

index do
  columns :id, ...
end
show do
  rows :id, ...
  table_for ... do
    columns ...
  end
end

I know rows and columns is NOT documented, but it's pretty useful, especially with decorators where the show.rows and index.columns only define what to show and decorators define how to show it (I'm using mine ArbreDecorator).

To make columns work - I had to do:

Arbre::Element::BuilderMethods.remove_method :columns

Now the question arises, is it worth documenting show.rows/index.columns and the trick to make columns work.

Going a step further could you consider extracting ActiveAdmin::Views::Columns to separate gem so it does not have to disabled but rather included with a note it affects index.columns behavior?

Optionally the Arbre::Element::BuilderMethods.columns method could detect if it's first (and second?) argument is a symbol and act as ActiveAdmin::Views::TableFor.columns otherwise act as ActiveAdmin::Views::Columns.

I can help out with any changes needed :)

WDYT?