title: how to collate an array of dictionaries into a dictionary of arrays?
body: <p>I have this data:</p>
  
  <pre><code>list = [
        {name:'apple', category: "fruit", price: 1.22 },
        {name:'pear', category: "fruit", price: 2.22 },
        {name:'coke', category: "drink", price: 3.33 },
       {name:'sprite', category: "drink", price: .44 },
      ];
  </code></pre>
  
  <p>And I'd like to create a dictionary keyed on category, whose value is an array that contains all the products of that category. My attempt to do this failed:</p>
  
  <pre><code>  var tmp = {};
      list.forEach(function(product) {
        var idx = product.category ;
        push tmp[idx], product;
      });
      tmp;
  </code></pre>