Ordered Count for each Unique Entry

[erahi]

I have data in longitudinal format for patients. Each row denotes a treatment with patient column for Patient ID and date of treatment. I need a formula to work out an ordered count for each patient for their first treatment, second treatment, third treatment etc.

 

[Yongle]

Patient ID	Date	Ordered Count	Explanation
Patient 1	25/05/2017	1	Patient 1 treatment 1
Patient 3	28/05/2017	1	Patient 3 treatment 1
Patient 1	03/06/2017	2	Patient 1 treatment 2
Patient 3	15/06/2017	2	Patient 3 treatment 2
Patient 4	18/07/2017	1	Patient 4 treatment 1
Patient 1	20/07/2017	3	Patient 1 treatment 3
Patient 1	23/07/2017	4	Patient 1 treatment 4
Patient 4	27/07/2017	2	Patient 4 treatment 2
Patient 3	15/08/2017	3	Patient 3 treatment 3
Patient 2	16/08/2017	1	Patient 2 treatment 1
Patient 1	10/09/2017	5	Patient 1 treatment 5
Patient 2	01/10/2017	2	Patient 2 treatment 2
Patient 3	12/10/2017	4	Patient 3 treatment 4
Patient 1	01/11/2017	6	Patient 1 treatment 6
Patient 2	04/11/2017	3	Patient 2 treatment 3

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The data can be sorted in any way, the formula continues to work

Formula in C2 copied down
=COUNTIFS(A:A,A2,B:B,"<"&B2)+1

Formula in D2 copied down
=A2&" treatment " &COUNTIFS(A:A,A2,B:B,"<"&B2)+1

 

[erahi]

Perfect! Exactly what I wanted, thanks so much