The Filter area of a Derived Dataset definition allows you to subset the records based on a condition you specify.
After opening the settings dialog for a derived dataset (see https://support.lityxiq.com/241959-EditingDefining-a-Dataset-View), follow these steps to define a filter. Note that it is not required that a derived dataset have a filter defined.
1) If the Filter panel is not already opened, click on that panel header to open it. Then, click the Edit button. Note that if this view had previously been defined, you will see information describing the currently defined filter displayed in this panel. To delete the filter, click the Delete button.
2) After clicking Edit, the Define Filter dialog appears. This is a common dialog in LityxIQ, and is explained in more detail in this article: https://support.lityxiq.com/806706-Using-the-Filter-Dialog
3) When finished, click Save, or click Cancel to cancel without saving changes. This will return you to the main settings dialog for the derived dataset.