Using each_slice to produce a table but with sub headings - ruby-on-rails

Question

I am using each_slice to output a two column table.
I would like to insert a title row when an attribute of the elements I am iterating changes.
I have :
all_users = Users.order('category, name asc').all
all_users.each_slice(2) do |two_users|
<tr>
<td style="text-align:right">
<%= two_users[0].category + ' - ' + two_users[0].name %>
</td>
<% if two_users[1].present? %>
<td>
<%= two_users[1].category + ' - ' + two_users[1].name %>
</td>
<td>
<% else %>
<td></td>
<% end %>
</tr>
<% end %>
And would like something like :
current_category = ''
all_users = Users.order('category, name asc').all
all_users.each_slice(2) do |two_users|
<% if two_users[0].category != current_category
current_category = two_users[0].category
%>
<tr><td colspan="2"><%= two_users[0].category %></td></tr>
<% end %>
<tr>
<td style="text-align:right">
<%= two_users[0].name %>
</td>
<% if two_users[1].present? %>
<td>
<%= two_users[1].name %>
</td>
<td>
<% else %>
<td></td>
<% end %>
</tr>
<% end %>
This doesn't work obviously in the case that two_users[1] has a new category.
I am trying to avoid the additional SQL queries of iterating through each category and requesting
the users for each independantly.

Answer 1

all_users.each_slice(2).with_object({cc: nil}) do |two_users, memo|
if category = two_users.detect { |u| u.category != memo[:cc] }
# print additional row or do whatever here
memo[:cc] = category
end
end
Enumerable#detect here returns either changed category or nil if there were no changes.
Sidenote: Try to DRY:
<td>
<%= two_users[1].name if two_users[1].present? %>
</td>