I have a list of objects: IList<O> O has several properties but only two of them are relevant: Date and Duration I want to "split" the list into several lists that contain only the objects that have matching Date and Duration Properties. Example: InitialList: 0- Date==1, Duration==7 1- Date==1, Duration==7 2- Date==2, Duration==7 3- Date==2, Duration==7 4- Date==2, Duration==14 5- Date==2, Duration==14 Desired result: IList<IList<O>: 0- 0- Date==1, Duration==7 1- Date==1, Duration==7 1- 0- Date==2, Duration==7 1- Date==2, Duration==7 2- 0- Date==2, Duration==14 1- Date==2, Duration==14 i know this can be done with some linq selects but am not sure how. thanks for the help.