cumulative sum by symbol, but with a cap on the value

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1

For example in the below table, I want to run the cumulative sum on “val” column of the table, grouped by the symbol column. but I want to cap the cumulative sum by the value in the “cap” column. If the cumulative sum exceeds the cap, I just cap it at that value. And for the next value, I will add it on up of the capped value:

Example  I am given input date, sym, val, cap, I want to produce the output in “cumval” column.

> `date sym val cap cumval``2020.01.01 AAPL 100 200 100``2020.01.02 AAPL 100 200 200``2020.01.03 AAPL 100 200 200``2020.01.04 AAPL -100 200 100``2020.01.01 MSFT 100 300 100``2020.01.02 MSFT 100 300 200``2020.01.03 MSFT 100 300 300``2020.01.04 MSFT 100 400 400`


  


  


for example on 2020.01.03, cumval of AAPL is capped at 200. and on 2020.01.04, we have 200-100 = 100 
2

q)update cumval:{min z,x+y}\[0;val;cap] by sym from tdate sym val cap cumval-------------------------------2020.01.01 AAPL 100 200 1002020.01.02 AAPL 100 200 2002020.01.03 AAPL 100 200 2002020.01.04 AAPL -100 200 1002020.01.01 MSFT 100 300 1002020.01.02 MSFT 100 300 2002020.01.03 MSFT 100 300 3002020.01.04 MSFT 100 400 400