Filter to be used with Twitter Bootstrap col-md's and row's. Can be optimized greatly but still work well

row.js

'use strict';

angular.module('dailymotionApp')
  .filter('col', function(){
    return function(input, numColumns){
      if(input !== undefined) {
        var filtered = [];
        for(var x = 0; x < input.length; x++){
          if(x % numColumns === 0){
            filtered.push(filtered.length);
          }
        }
        return filtered;
      }
    }
  }).filter('row', function(){
    return function(input, row, numColumns){
      if(input !== undefined) {
        var returnArray = [];
        for(var x = row * numColumns; x < row * numColumns + numColumns; x++){
          if(x < input.length){
            returnArray.push(input[x]);
          }
          else{
            returnArray.push("");
          }
        }
        return returnArray;
      }
    }
  });