Hello Javiera Meneses,
sorry for so long delay, but I could find the solution. In order to display only sections with events, please follow these general steps:
1). Every time the onViewChange fires the value of the collection of the list property should be changed according to the actual events:
https://docs.dhtmlx.com/scheduler/api__scheduler_onviewchange_event.html
2). You can take the actual events via getEvents() and change the collection via serverList and updateCollection() methods.
3). You can keep the current sections in the hash table, which is updated every time you change the view.
Please, see the working sample:
https://snippet.dhtmlx.com/5/ef1fdcddc