Calculating moving average over irregular data - sql

Question

I am trying to calculate a moving average of several fields in a SQL Server database that involved irregularly-spaced values over time. I realized that for regularly-spaced data I can use an SELECT grp, AVG(count) FROM t ... OVER (PARTITION BY grp ... ROWS 7 PRECEDING) to create a moving average of the prior week's data. However, I have data organized as follows:
DATE GRP COUNT
2018-07-05 1 10
2018-07-08 1 4
2018-07-11 1 6
2018-07-12 1 6
2018-07-11 2 5
2018-07-15 2 10
2018-07-17 2 8
2018-07-20 2 10
...
Where for most groups there are no observations for some dates. The output I'm looking for is:
DATE GRP MOVING_AVG
2018-07-05 1 10
2018-07-08 1 7
2018-07-11 1 6.67
2018-07-13 1 5.33
2018-07-11 2 5
2018-07-15 2 7.5
2018-07-16 2 7.67
2018-07-20 2 9.33
Is there a way of specifying dates instead of rows in the PRECEDING clause, or do I have to create some sort of mask to average over?
EDITED FOR CLARIFICATION BASED ON COMMENTS

Answer 1

In SQL Server, I think this might be simpler achieved with a lateral join:
select
date,
grp,
(
select avg(count)
from mytable t1
where
t1.grp = t.grp
and t1.date >= dateadd(year, -1, t.date)
and t1.date <= t.date
) as cnt
from mytable

Answer 2

If i'm not misunderstanding. You want 7 or whatever days but rows before a date.
DATE GRP COUNT
2018-07-11 2 5
2018-07-15 2 10
2018-07-17 2 8
2018-07-20 2 10 <--- the AVG of this row must include 7 days before,so 2018-07-11 not include
In that case :
select
date,
grp,
(
select avg(count)
from t t1
where
t1.grp = t.grp
and DATEDIFF(day, t1.date, t.date) <= 7 /*7 or whatever day you want*/
and t1.date <= t.date
) as MOVING_AVG
from t