average of 2 columns subtraction

[rexhina]

I have a table in Qlik sense and I want to find the average of the difference between two columns. The table is like this :

I want to write a function to find the average of the difference between two columns. I have tried something like this : 

avg(aggr(if(not is null (day 1) and not is null(day2),day2-day1)),customer  name ) 

but it is not working.  Help me with this

Day 1	Day 2	Average of difference between the day2 and day1
24.11.2021	27.11.2021
12.12.2021
13.12.2021	18.12.2021
	17.1.2022
3.1.2022	7.1.220

[rexhina · Accepted solution]

i have found the solution myself it will be the formula like this :

avg(aggr(if(not is null (day 1) and not is null(day2),(day2-day1))),day2,day1 )