In Radiant, group children in N slices

gistfile1.html

<r:children:slice slices="2">
  <ul>
    <r:each>
      <li><r:title /></li>
    </r:each>
  </ul>
</r:children:slice>

gistfile2.rb

  desc %{
    Slices children in N different groups
    *Usage:*
    <pre><code><r:children:slice [slices="number"]>
    ...
    </r:children:slice>
    </code></pre>
  }
  tag 'children:slice' do |tag|
    result = []
    children = tag.locals.children

    slices = tag.attr['slices'].to_i || 2
    slice = (children.size.to_f / slices).ceil
    
    children.each_slice(slice) do |children_slice|
      tag.locals.children_slice = children_slice
      result << tag.expand
    end

    result
  end

  tag 'children:slice:each' do |tag|
    result = []
    tag.locals.children_slice.each do |item|
      tag.locals.child = item
      tag.locals.page = item
      result << tag.expand
    end

    result
  end