Re-using the FirstSortedValue on subsequent rows

[tvanlaun]

Hi experts

In my data set, I'm trying to get the earliest stock price for each stock, based on the users' selections of both stocks and dates.  This is so I can show a % movement, always starting with a base of 100% for each stock, regardless of the user's selection.

Below is a sample data set and how I'd like the output to look.

I've got as far as FirstVal = aggr(FirstSortedValue(Close,Date),Co)

(I'm not sure why this appears only on the second line!)

What I would like to understand is:  How do I get the First Val on to every line, so that I can use it to calculate the stock price re-based to the user's date range?

Many thanks!

Date	Co	Close	First Val
21/03/2017	Co A	84.42	-
22/03/2017	Co A	82.71	84.42
23/03/2017	Co A	82.95	-
24/03/2017	Co A	83.38	-
27/03/2017	Co A	83.4	-
28/03/2017	Co A	85.26	-
29/03/2017	Co A	86.14	-
21/03/2017	Co B	43.92	-
22/03/2017	Co B	43.29	43.92
23/03/2017	Co B	43.4	-
24/03/2017	Co B	43.88	-
27/03/2017	Co B	44	-
28/03/2017	Co B	44.38	-
29/03/2017	Co B	44.88	-
21/03/2017	Co C	34.32	-
22/03/2017	Co C	33.49	34.32
23/03/2017	Co C	33.44	-
24/03/2017	Co C	33.9	-
27/03/2017	Co C	34	-
28/03/2017	Co C	34.7	-
29/03/2017	Co C	35.14	-
21/03/2017	Co D	25.82	-
22/03/2017	Co D	25.43	25.82
23/03/2017	Co D	25.61	-
24/03/2017	Co D	25.94	-
27/03/2017	Co D	25.94	-
28/03/2017	Co D	26.25	-
29/03/2017	Co D	26.35	-

[tvanlaun]

Answered my own question!  I posted this after ages trying to crack it.  As soon as I returned to the problem after posting, I figured it out:

aggr( NODISTINCT FirstSortedValue(Close,Date),Co)

Hope this helps someone in the future.