Rails 3. Get totals from array - ruby-on-rails

Question

I'm printing out a table with line totals but I also want to get the grand total of the columns. This following code doesn't work, instead of the grand totals it just prints out the values of the last iteration.
<% #shipments.each do |shipment| %>
<tr>
<td style="text-align:center;"><%= shipment.file_number %></td>
<td><%= shipment.shipper.company_name %></td>
<td><%= shipment.hbl %></td>
<td><%= shipment.status %></td>
<td><%= shipment.age %></td>
<td><%= shipment.invoice.read_issued_at unless shipment.invoice.nil? %></td>
<td><%= number_to_currency shipment.invoice.customer_total unless shipment.invoice.nil? %></td>
<td><%= number_to_currency shipment.invoice.customer_amount_paid unless shipment.invoice.nil? %></td>
<td><%= number_to_currency shipment.invoice.customer_open_balance unless shipment.invoice.nil? %></td>
</tr>
<%
grand_customer_total = 0
grand_customer_amount_paid = 0
grand_customer_open_balance = 0
grand_customer_total += shipment.invoice.customer_total
grand_customer_amount_paid += shipment.invoice.customer_amount_paid
grand_customer_open_balance += shipment.invoice.customer_open_balance
%>
<% if #shipments.last == shipment %>
<tr>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<th>Totals</th>
<td><%= number_to_currency grand_customer_total %></td>
<td><%= number_to_currency grand_customer_amount_paid %></td>
<td><%= number_to_currency grand_customer_open_balance %></td>
</tr>
<% end %>

Answer 1

The reason your code isn't working is that your variables are defined in the block, so they're considered block-local variables. Once the block is exited those variables are marked to be cleared; each iteration re-defines those variables. It also doesn't help that you're reassigning them to 0 on each iteration, but that isn't even coming into effect here because the variables aren't defined each time through.
You could simply define the variables before the block, but that's still pretty messy. Since Ruby idioms and conventions put an emphasis on clean and well-organized code, I'd stray away from that and instead calculate these numbers separately, possibly in your controller.
#totals = {
:overall => #shipments.reduce(0) { |total, shipment| total + shipment.invoice.customer_total },
:paid => #shipments.reduce(0) { |total, shipment| total + shipment.invoice.customer_amount_paid },
:balance => #shipments.reduce(0) { |total, shipment| total + shipment.invoice.customer_open_balance }
}
Then, instead of using #shipments.last comparison, you can just do the following after your shipments table output:
<tr>
<td colspan="5"></td>
<th>Totals</th>
<td><%= number_to_currency #totals[:overall] %></td>
<td><%= number_to_currency #totals[:paid] %></td>
<td><%= number_to_currency #totals[:balance] %></td>
</tr>

Answer 2

You set the grand total to zero every time through the loop. move the initialization up before the loop.

Answer 3

you can use ruby inject
something like
#shipments.inject(0) { |sum, shipment| sum + shipment.invoice.customer_total }
or to keep with your code layout, just initialize the grand_customer_* objects outside of the #shipments.each loop because you are resetting them every time through

Answer 4

<%
grand_customer_total = 0
grand_customer_amount_paid = 0
grand_customer_open_balance = 0
%>
<% #shipments.each do |shipment| %>
<tr>
<td style="text-align:center;"><%= shipment.file_number %></td>
<td><%= shipment.shipper.company_name %></td>
<td><%= shipment.hbl %></td>
<td><%= shipment.status %></td>
<td><%= shipment.age %></td>
<td><%= shipment.invoice.read_issued_at unless shipment.invoice.nil? %></td>
<td><%= number_to_currency shipment.invoice.customer_total unless shipment.invoice.nil? %></td>
<td><%= number_to_currency shipment.invoice.customer_amount_paid unless shipment.invoice.nil? %></td>
<td><%= number_to_currency shipment.invoice.customer_open_balance unless shipment.invoice.nil? %></td>
</tr>
<%
grand_customer_total += shipment.invoice.customer_total
grand_customer_amount_paid += shipment.invoice.customer_amount_paid
grand_customer_open_balance += shipment.invoice.customer_open_balance
%>
<% if #shipments.last == shipment %>
<tr>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<th>Totals</th>
<td><%= number_to_currency grand_customer_total %></td>
<td><%= number_to_currency grand_customer_amount_paid %></td>
<td><%= number_to_currency grand_customer_open_balance %></td>
</tr>
<% end %>