Good morning.   The below dataset I have all but the Wanted column. That is what I require. So for every first.reference the Wanted should be 1. For the next reference, if it is the same value as the reference in the line above, check the FLAG value. If it is the same as the line above, it should be the same as the Wanted value above. If the FLAG value is different from the line above (i.e. from 0 to 1 or 1 to 0), the WANTED value should be lag(Wanted )+ 1. DO that until the next Reference and if it is the first reference start again.   I have tried so many pieces of code. The lag creates a blank. Also the lag when using a loop seems to keep an old version of the lag. I am just unsure as to where to start...   Ta, Arch   Month_A Month_B Reference Date_C FLAG Wanted Nov-23 Jan-24 A 2/11/2023 1 1 Oct-22 Jul-23 B 3/10/2022 1 1 Nov-23 Jan-24 B 3/10/2022 0 2 May-23 Jan-24 C 15/05/2023 1 1 Feb-23 Sep-23 D 9/02/2023 1 1 Oct-23 Jan-24 D 9/02/2023 0 2 May-23 Dec-23 E 30/05/2023 1 1 Mar-23 Mar-23 F 14/03/2023 1 1 Apr-23 Jun-23 F 27/04/2023 1 1 Jul-23 Jan-24 F 27/04/2023 0 2 May-23 May-23 G 31/05/2023 1 1 Mar-23 Apr-23 H 6/03/2023 1 1 May-23 Nov-23 H 6/03/2023 0 2 Dec-23 Jan-24 H 5/12/2023 1 3 ... View more