Rails Loop Through ActiveRecord By Attribute Value - ruby-on-rails-3

Question

Lets say I have an array of Match objects, each belonging to a round in a round robin tournament structure...
Matches
Round | Registrant_ID |Registrant_ID_2 |Winner_id
1 | 1 | 2 | 2
1 | 3 | 4 | 4
1 | 5 | 6 | 5
1 | 7 | 8 | 8
2 | 1 | 4 | 1
2 | 3 | 6 | 3
2 | 5 | 8 | 5
2 | 7 | 2 | 2
3 | 1 | 6 | 1
...
What I wish to do is group all of the matches by Round and loop through that round and list the matches.
The desired output would be something like...
<h1>Round 1</h1>
<table>
<thead>
<tr>
<th>Player 1</th>
<th>Player 2</th>
<th>Winner</th>
</tr>
</thead>
<tbody>
<tr>
<td>1</td>
<td>2</td>
<td>2</td>
</tr>
<tr>
<td>3</td>
<td>4</td>
<td>4</td>
</tr>
<tr>
<td>5</td>
<td>6</td>
<td>5</td>
</tr>
<tr>
<td>7</td>
<td>8</td>
<td>8</td>
</tr>
</tbody>
</table>
The problem I'm facing is that I don't know how to loop through the match records by their round attribute. I'm not sure if something like in_groups_of can be used because the number of players that participate in a round will vary, it won't always be 8 as seen here.
Here is my code thus far which simply loops through all records and creates a table for every match(I'm looking for tables for individual rounds):
- #matches.each do |match|
%h1= "Round #{match.round}"
%table.table.table-bordered
%thead
%tr
%th.span4 Player 1
%th.span4 Player 2
%th.span4 Winner
%tbody
%tr
%td= match.register.user.username
%td= match.register_2.user.username
%td= match.winner.user.username unless match.winner.nil?
Here's what the output is meant to look like, notice separate tables for separate rounds:

Answer 1

Maybe you mean to group matches by round, like this:
- #matches.group_by(&:round).each do |round, matches|
%h1= "Round #{round}"
%table.table.table-bordered
%thead
%tr
%th.span4 Player 1
%th.span4 Player 2
%th.span4 Winner
%tbody
- matches.each do |match|
%tr
%td= match.register.user.username
%td= match.register_2.user.username
%td= match.winner.user.username unless match.winner.nil?