How to create a non-static HTML table header and rows - ruby-on-rails

Question

I have two arrays, and I'd like to create a table with dynamic header cells (from the first array called subjects) and iteratively add contents (from the second array called examscores) in table rows with respect to the table header value.
Desired outcome is (fiddle):
The erb code is:
<table width="100%" border="1">
<thead>
<tr>
<th rowspan="2" scope="col">NAME</th>
<th colspan="<%= #subjects_by_class.size %>" scope="col">Subjects/Scores</th>
<th rowspan="2" scope="col">Total</th>
<th rowspan="2" scope="col">Average</th>
</tr>
<tr>
<% #subjects_by_class.each do |s| %>
<th> <%= s.name %></th>
<% end %>
</tr>
</thead>
<tbody>
<% #examscore.each do |ex| %>
<tr>
<td><%= get_student_name_by_id(ex.student_id) %></td>
<% #subjects_by_class.each do |ss| %>
<% #examscore.each do |ii| %>
<% if ss.id == ex.subject_id %>
<td> <%= i.total %> </td>
<% break %>
<% end %>
<% end %>
<% end %>
<td><%= sum_student_totalscore(ex.student_id, year_id) %> </td>
<td><%= avg_student_totalscore(ex.student_id, year_id) %></td>
</tr>
<% end %>
</tbody>
</table>
The output I get is (fiddle):
A new tr is created under Maths subject instead of a new td for Arts subject, and this results in Average td being distorted.
Any insight will be greatly appreciated.

Answer 1

Well, just look at this section of your code:
<% #examscore.each do |ex| %>
<tr>
You create a new line for each #examscore, and you have 4 of those (1 per user/subject, so you end up with 4 lines of course).
Your tbody should be something like this:
<tbody>
<% #students.each do |student| %>
<tr>
<td><%= student.name %></td>
<% #subjects_by_class.each do |subject| %>
<% #examscore.each do |score| %>
<% if score.subject_id == subject.id && score.student_id == student.id %>
<td><%= score.total %></td>
<% break %>
<% end %>
<% end %>
<% end %>
<td><%= sum_student_totalscore(student.id, year_id) %> </td>
<td><%= avg_student_totalscore(student.id, year_id) %></td>
</tr>
<% end %>
</tbody>
It's a bit strange that you only care about the year in your totals
Also you could improve things a little bit by having a method in your Student class that returns an array of scores for a given year/list of subjects
# Returns an array of scores for the given year
def scores(year, subject_ids)
subject_ids.map do |subject_id|
# find score for year & the given subject_id
end
end
This way your body would become
<tbody>
<% #students.each do |student| %>
<tr>
<td><%= student.name %></td>
<% #scores = student.scores(year_id, #subjects_by_class) %>
<% #scores.each do |score| %>
<td><%= score.total %></td>
<% end %>
<% scores_total = #scores.sum(&:total) %>
<td><%= scores_total %> </td>
<td><%= scores_total / #scores.size.to_f %></td>
</tr>
<% end %>
</tbody>
which I found more clear, but it could be further improved with decorators for instance.