Adding index number based on category

[Anonymous]

Hello, folks!

How can I add an index number that runs based on category type stated in another column? See the example picture. This is what I want to achiecve. I'd like the index column to give a number-series to all categories seperatly. Essentialy I would then be able to sort on category and get a continous series running from 1 to "whatever-number".

Aditionally I would like the index series in each category to run according to date in another column.

Date	Category	Index
15.03.2018	Child	1
12.04.2018	Adult	2
13.04.2018	Adult	3
02.04.2018	Adult	1
25.06.2018	Child	2
22.05.2018	Adult	4
27.09.2018	Child	4
22.08.2018	Child	3
15.10.2018	Child	5
02.10.2018	Adult	5

Is there any way to do this? I found this this forum-post interesting, but I can't really get it to fit my goal exactly. However, maybe some of you understand how to use this info for my purpose.

 

Best:

- Per-J.H.