gud day how can i make a running total fields per group per year?

ex. Fields are: Code,Amount,Year,RtotalField(for computation)

Code|| Amount|| Year|| RTotalField(new specified field)
AAAA|| 100000|| 1998|| 100000
AAAA|| 200000|| 1999|| 300000 (Added from Amount of 1998 of this code)
AAAA|| 300000|| 2000|| 600000 (Added from Amount of 1998 to this year per code)
BBBB|| 100000|| 1998|| 100000
BBBB|| 100000|| 2000|| 200000 (Added from Amount of 1998 of this code)
CCCC|| 100000|| 1999|| 100000

* everytime new year reads the running total field change per code

Hope you could help me through this, tks.

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