Hi, Mina. Undo/Redo functionality is limited in the Data Editor. Certainly once you have passed the data by computing a variable and running it, undoing that will not be possible using Edit>Undo. If you have a copy of the data on disk, you can "revert" to the latest saved copy by selecting File>Open>Data and re-opening it.
In v27 and later, you can also have the ability to save "restore points."
------------------------------
Rick Marcantonio
Quality Assurance
IBM
------------------------------