Resolved: pandas increment under specific condition of other column

Question:

Given dataframe
how to get result like in column B?
The idea is when column A row is equal with column A previous row, add 1, else back to 0
I’ve tried:
however, the result that i got is [0,0,1,1,1,0] instead
do i missed some steps or non logical operation here?
any hint will be very helpful
thank you in advance

Answer:

Let us try groupby and cumcount:

If you have better answer, please add a comment about this, thank you!