so#47803473

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  items: [{id:1},{id:2},{id:3},{id:4},{id:5},{id:6}],
  rowCount: Ember.computed('items.length', function() {
    return this.get('items.length')/3;
  })
});

helpers.get-item-at-array-index.js

import Ember from 'ember';

export function getItemAtArrayIndex(params/*, hash*/) {
  let array = params[0];
  let index = params[1];
  let rowIndex = params[2];
  
  return array[index+rowIndex*3];
}

export default Ember.Helper.helper(getItemAtArrayIndex);

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}

<table>
	{{#each (range 0 rowCount) as |rowIndex|}}
  	<tr>
    {{#each (range 0 3) as |columnIndex|}}
  		{{! `number` will go from 0 to 2}}
      <td>
      	{{get (get-item-at-array-index items columnIndex rowIndex) 'id'}}
      </td>
		{{/each}}
    </tr>
	{{/each}}
</table>
<br> 
<br>

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-composable-helpers":"2.0.3"
  }
}