Make Rows with large data set in Jade Templating in Node.js

I have about 100 items that I use jade iteration to write each one of them to html. However, I'm struggling to find an elegant way to separate the items into rows of three.

To be clear, I want something like this:

.row
    .item1
    .item2
    .item3
.row
    .item1

... and so on...

I've tried things with inline javascript like this with no luck:

- var a = 0;
  each item in list
    - a++;
    - if(a % 3 == 0)
      .row-fluid
        .span3(id='#{item.id}')
          p #{item.id}
    - else
        .span3(id='#{item.id}')
          p #{item.id}

note: this kills the list

while list.length > 0
  .row
    for item in list.splice(0, 3)
      .span3(id=item.id)
        p= item.id

let me know if this works as i just wrote it off the top of my head

- var i = -3;
while i <= list.length
  - i += 3;
  .row
    each item in list.slice(i, i+3)
      .span3(id='#{item.id}')