ustomer.Id,
                                Name = customer.Name,
                                Cost = order.Cost, 
                            });
</code></pre>
<h2 id="grouping">Grouping</h2>
<pre><code class="language-csharp">var grouped = orders.GroupBy(order =&gt; CustomerId);
</code></pre>
<p>Note: Result will be an <code>IGrouping&lt;TKey,TElement&gt;</code></p>
<h2 id="lookup">Lookup</h2>
<pre><code class="language-csharp">var packagesByCompany = packages.ToLookup(oder =&gt; oder.Date,  order =&gt