Transpose, Slice and Inject From Multipe Arrays - ruby-on-rails

Question

I don't know how appropriate title for this question.
Well, This is my problem
I have index action on homes_controller.rb looks like :
def index
#r = 2
#datas = [[1, 10], [2, 10], [3, 15], [4, 20], [5, 70], [6, 180], [7, 250], [8, 270], [9, 230], [10, 40], [11, 0], [12, 10]]
end
I want to result from above like this:
And on view looks like :
<table>
<thead>
<tr>
<th>Month</th>
<th>Forecast</th>
<th>Order</th>
<th>Begining Inventory</th>
<th>Ending Inventory</th>
</tr>
</thead>
<tbody>
<% ei = 0 %>
<% #datas.each_with_index do |d, index| %>
<tr>
<td><%= d[0] %></td>
<td><%= d[1] %></td>
<td><% if d[1] > bi %>
<% #datas.transpose.at(1).slice(index, #r).inject do |sum, s| -%>
<%= #biu = sum + s %>
<% end %>
<% end %>
</td>
<td><%= #bi = ei + #biu %></td>
<td><%= #ei = #bi - d[1] %></td>
</tr>
<% #biu = 0 %>
<% ei = #ei %>
<% end %>
</tbody>
</table>
State :
When the forecast d[1] is bigger than ei the calculation order #biu is 2 (#r) next of forecast.
Begining Inventory #bi is calculation from ei plus order #biu
Ending Inventory #ei is calculation from #bisubtracted with forecast d[1]
And then #ei put to ei
But the result like this :
I want 12th months must have : Order = 10, Begining invetory = 10, and Ending Inventory = 0

Answer 1

Your problem is here:
<% #datas.transpose.at(1).slice(index, #r).inject do |sum, s| -%>
<%= #biu = sum + s %>
<% end %>
When an array has only one item, inject without a starting value does not run the block at all:
puts [1,2].inject { |sum, s| puts 'was here!'; sum + s }
# was here!
# 3
puts [1].inject { |sum, s| puts 'was here!'; sum + s }
# 1
puts [1].inject(0) { |sum, s| puts 'was here!'; sum + s }
# was here!
# 1
If you add a starting value 0 to your code, though, #biu will be printed twice. To avoid that you need to move the assignment outside of the block:
<% #biu = #datas.transpose.at(1).slice(index, #r).inject do |sum, s| -%>
<% sum + s %>
<% end %>
<%= #biu %>
Or, more succinctly:
<%= #biu = #datas.transpose.at(1).slice(index, #r).inject(:+) %>