Date difference between pairs of dates per ID

Question

I have data with 2 columns, in the following format:

ID	Date
1	1/1/2020
1	27/7/2020
1	15/3/2021
2	18/1/2020
3	1/1/2020
3	3/8/2020
3	18/9/2021
2	23/8/2020
2	30/2/2021

Now I would like to create a calculation field in Tableau to find per ID the difference between the different dates. For any value eg days.

For example for ID 1 the difference of the two dates according to calendar is 208 days. Next the difference of the second to third date for the same ID is 231 days.

Answer 1

A table calc like the following should do if you get the partitioning, addressing and ordering right — such as setting “compute using” to Date.

If first() < 0 then min([Date]) - lookup(min([Date]), -1) end