Rails summary with sub-totals by date - ruby-on-rails

Question

I'm writing my first Rails view that summarizes data by date. I want one row for each date with the columns summarized for that date.
I have been able to make it work. But, it's awkward coding. This is what I have:
<h3>Carwings Daily Summary</h3>
<table class="display dataTable table table-striped table-bordered" id="dataTable2">
<thead>
<tr>
<th>Date</th>
<th># Trips</th>
<th>E Consumption (kWh)</th>
<th>E Regeneration (kWh)</th>
<th>E Total (kWh)</th>
<th>Distance (Miles)</th>
<th>Energy Economy (Miles/kWh)</th>
<th>CO2 Emission Reduction (lbs)</th>
</tr>
</thead>
<tbody>
<% trips = 0 %>
<% consumption = 0 %>
<% regen = 0 %>
<% total = 0 %>
<% distance = 0 %>
<% economy = 0 %>
<% emissions = 0 %>
<% sumdate = nil %>
<% #carwings.each.with_index do |carwing, index| %>
<% sumdate = carwing.date if index == 0 %>
<% if carwing.date == sumdate %>
<% trips = trips + 1 %>
<% consumption = consumption + carwing.e_consumption %>
<% regen = regen + carwing.e_regen %>
<% total = total + carwing.e_total %>
<% distance = distance + carwing.distance %>
<% economy = economy + carwing.economy %>
<% emissions = emissions + carwing.emission_reduction %>
<% else %>
<tr>
<td class="nowrap"><%= sumdate %></td>
<td><%= trips %></td>
<td><%= consumption %></td>
<td><%= regen %></td>
<td><%= total %></td>
<td><%= distance %></td>
<td><%= economy %></td>
<td><%= emissions %></td>
</tr>
<% trips = 1 %>
<% consumption = carwing.e_consumption %>
<% regen = carwing.e_regen %>
<% total = carwing.e_total %>
<% distance = carwing.distance %>
<% economy = carwing.economy %>
<% emissions = carwing.emission_reduction %>
<% sumdate = carwing.date %>
<% end %>
<% end %>
<tr>
<td class="nowrap"><%= sumdate %></td>
<td><%= trips %></td>
<td><%= consumption %></td>
<td><%= regen %></td>
<td><%= total %></td>
<td><%= distance %></td>
<td><%= economy %></td>
<td><%= emissions %></td>
</tr>
</tbody>
</table>
There's got to be a better way.
Suggestions?
Thanks for the Help!!

Answer 1

Some minor stuff:
trips = trips + 1
# is better written as:
trips += 1
erb tags can be multiline eg:
<% if blah
do_something
something else
end %>
If you are setting multiple variables to the same value, you don't need to repeat them each line eg:
trips = consumption = regen = 0
yes - this is minor stuff - but clean up the minor stuff and it'll give you a better shape of what you're trying to do.
perhaps if you gave us your logic in descriptive pseudocode (so we aren't just guessing what you're trying to do) then we can give you better structure to your code too. :)
Personally: I'd recommend setting up all this data in your controller (or even your carwing model) before it ever hits the view. I'd use a hash - whee the carwnig.date is the key, and all the rest is another hash eg:
data = Hash.new({:trips => 0, :consumption => 0}) # google initialising hashes
#carwings.each do |carwing|
data[carwing.date][:trips] += 1
data[carwing.date][:consumption] += carwing.e_consumption
# etc
end