What happens if we change the number of datasets in the array? To test this, let's add a new helper function (called set()) to randomly generate a new set of data with a random number of elements between 1 and 10:

    var set = function() { 
      var k = rand(); 
      var d = []; 
      for (var i = 1; i < k; i++) { 
        d.push[i]; 
      }; 
      return d; 
    }; 

Modify the data function slightly. We will print to the console to validate that it is working properly:

    var data = function() { 
      var d = set(); 
      console.log('d', d); 
      return d.map(function(d,i) { 
        var cost = rand(); 
        var sales = rand(); 
 
        return { 
          category: 'category-'+i, 
          cost: cost, 
          sales: cost + sales 
        }; 
      }); 
    }; 

Now, if we look at http://localhost:8080 again, we can see that the visualization is working properly even with a random amount of data.