Delta(difference) between two selected columns

[nezuko_kamado]

How can I create a column that calculates the differences between selected table columns?

For example, if I select week1 and week3, the difference should be calculated at the last column.

original:
load * inline [ Date, Week, ID, Unit
9/1/2021, 1, A, 1
9/1/2021, 1, A, 2
9/2/2021, 1, A, 1
9/2/2021, 1, A, 2
9/2/2021, 1, C, 2
9/3/2021, 1, A, 1
9/4/2021, 1, A, 2
9/5/2021, 1, A, 2
9/6/2021, 1, A, 2
9/7/2021, 2, A, 3
9/9/2021, 2, A, 3
9/9/2021, 2, A, 3
9/9/2021, 2, C, 3
9/3/2021, 1, B, 1
9/4/2021, 1, B, 2
9/5/2021, 1, B, 2
9/6/2021, 1, B, 2
9/7/2021, 2, B, 3
9/7/2021, 2, B, 5
9/7/2021, 2, C, 5
9/9/2021, 2, B, 3
9/10/2021, 2, A, 3
9/14/2021, 3, A, 2
9/10/2021, 2, B, 3
9/11/2021, 3, B, 2
9/12/2021, 3, B, 2
9/13/2021, 3, B, 2
9/13/2021, 3, B, 4
9/14/2021, 3, B, 2
9/27/2021, 5, A, 2
9/28/2021, 5, A, 5
9/15/2021, 3, B, 2
9/15/2021, 3, B, 3
9/16/2021, 3, B, 2
9/1/2022, 1, A, 2
9/1/2022, 1, A, 3
9/2/2022, 1, A, 4
9/2/2022, 1, A, 5
9/2/2022, 1, C, 6
9/3/2022, 1, A, 7
9/4/2022, 1, A, 8
9/5/2022, 1, C, 8
9/6/2022, 1, C, 2
9/7/2022, 2, A, 3
9/9/2022, 2, A, 3
9/9/2022, 2, A, 4
9/9/2022, 2, C, 4
9/3/2022, 1, B, 6
9/4/2022, 1, B, 1
9/5/2022, 1, B, 7
9/6/2022, 1, A, 2
9/7/2022, 2, B, 3
9/7/2022, 2, B, 4
9/7/2022, 2, C, 2
9/9/2022, 2, C, 1
9/10/2022, 2, A, 3
9/14/2022, 3, A, 2
9/10/2022, 2, B, 3
9/11/2022, 3, B, 2
9/12/2022, 3, B, 2
9/13/2022, 3, B, 2
9/13/2022, 3, B, 4
9/14/2022, 3, B, 2
];

[Taoufiq_Zarra]

@nezuko_kamado  can you share the expected output

[nezuko_kamado]

I want to create a column that calculates the delta of whatever selected two columns.  

Thank you so much!