WPF datagrid grouping <p>I'm grouping my grid like this:</p> <pre><code>ListCollectionView collection = new ListCollectionView(_ActionCollection); collection.GroupDescriptions.Add(new PropertyGroupDescription("InvoiceNumber")); dataGrid1.ItemsSource = collection; </code></pre> <p>Now I want to get the sum of the items which are grouped.</p> <p>For example:</p> <p>If grouped ivnoice number 231 and 245 contain both 3 rows, how can I get the sum for the example id?</p>