Calculating Average number of days between sessions

[s_a_chari]

Hello!

I’m pretty new to looker, so please bear with me!

I’m trying to calculate the average number of days between sessions/logins of users. The data looks something like this:
 

Where each row corresponds to a user.

As an example of the result I’d like for each row:
The result for Row 1 would be: 2
The result for Row 2 would be : 7/3 = 2.33, i.e (number of days w/ no sessions/ no. of groups of no session days).

How might I go about this in the table calculator?

Cheers!