Extjs 4 - Combining two grid columns

Use a custom renderer:

{
   header: "Name",
   dataIndex: 'last_name',
   renderer: function(value, element, record) {
       return record.data['last_name'] + ', ' + record.data['first_name'];
   }
}

you can use templeteColumn for it which is a Column definition class which renders a value by processing a Model's data using a configured XTemplate

http://docs.sencha.com/ext-js/4-0/#/api/Ext.grid.column.Template