Hi,

I think you can follow these steps:

1. Use window function to create a new column by shifting, then your df will look like this

id value lag

1 A-B-C-D-E-F null

2 A-B-G-C-D-E-F A-B-C-D-E-F

3 A-B-G-D-E-F A-B-G-C-D-E-F

2. Use split() to convert string to array.

id value lag

1 ['A', 'B', 'C', 'D', 'E', 'F'] null

2 ['A', 'B', 'G', 'C', 'D', 'E', 'F'] ['A', 'B', 'C', 'D', 'E', 'F']

3 ['A', 'B', 'G', 'D', 'E', 'F'] ['A', 'B', 'G', 'C', 'D', 'E', 'F']

3. Create a column using array_except('value', 'lag') to find element in column 'value' but not in column 'lag'

4. Create a column using array_except('lag', 'value') to find element in column 'lag' but not in column 'value'

5. Then, you concat these two columns above, you will have the comparison.

Hope it works.