title: ActiveAdmin: how to add second custom index table page
body: <p>Users of some admin need to have two table views of, say, a model <code>Bar</code>: default one they already have and an additional new one with different set of columns.</p>
  
  <p>The setting is such:</p>
  
  <pre><code>ActiveAdmin.register Bar do
    # …
    index do
      column :name
      column :phone
      column :address
    end
    # …
  </code></pre>
  
  <p>It's expected to be as easy as adding another <code>index</code> block as in:</p>
  
  <pre><code>ActiveAdmin.register Bar do
    # …
    index do
      column :name
      column :price
      column :bartender
    end
  
    index name: 'location' do
      column :name
      column :phone
      column :city
      column :country
    end
  </code></pre>
  
  <p>and then just get the additional tab somewhere.</p>
  
  <p>As you may guess it is not that simple. ActiveAdmin nows nothing about the imaginary <code>index name:</code> attribute and just selects the first <code>index</code> block silently ignoring the second <code>index</code> block.</p>
  
  <p>ActiveAdmin documentation shows a way to <a href="http://activeadmin.info/docs/3-index-pages.html" rel="nofollow">add second/third/etc index page</a> with ease but of a different kind:</p>
  
  <pre><code>index as: :grid do |bar|
    link_to(image_tag(bar.photo_path), admin_bar_path(bar))
  end
  </code></pre>
  
  <p>Nice, but how to add a duplicate of the index table view with different columns?</p>