Creating calculated variables in one datastep - loops

Question

Any help is much appreciated. Thanks
I would like to create a couple of variables with my transactional data
I am trying to create variables 'act_bal' and 'penalty' using amount, type and Op_Bal. The rules I have are:
For the first record, the id will have op_bal and it will be
subtracted from the 'amount' for type=C and added if type=D to
calculate act_bal
For the second record onwards it is act_bal + amount for type=C and
act_bal-amount for type=D
I will add the penalty 10 only if the amount is >4 and the type=D.
The id can have only two penalties.
Total Penalty should be subtracted from the act_bal of the last
record which would become op_bal for the next day. (e.g. for id
101, -178-20=-198 will become the op_bal for 4/2/2019)
This is the data I have for two customers IDs 101 and 102 for two different dates (My actual dataset has the data for all the 30 days).
id date amount type Op_Bal
101 4/1/2019 50 C 100
101 4/1/2019 25 D
101 4/1/2019 75 D
101 4/1/2019 3 D
101 4/1/2019 75 D
101 4/1/2019 75 D
101 4/2/2019 100 C
101 4/2/2019 125 D
101 4/2/2019 150 D
102 4/1/2019 50 C 125
102 4/1/2019 125 C
102 4/2/2019 250 D
102 4/2/2019 10 D
The code I wrote is like this
data want;
set have;
by id date;
if first.id or first.date then do;
if first.id then do;
if type='C' then act_bal=Op_Bal - amount;
if type='D' then act_bal=Op_Bal + amount;
end;
else do;
retain act_bal;
if type='C' then act_bal=act_bal + amount;
if type='D' then act_bal=act_bal - amount;
if amount>4 and type='D' then do;
penalty=10;
end;
run;
I couldn't create a counter to control the penalties to 2 and could not subtract the total penalty amount from the amount of the last row. Could someone help me in receiving the desired result? Thanks
id date amount type Op_Bal act_bal penalty
101 4/1/2019 50 C 200 150 0
101 4/1/2019 25 D 125 0
101 4/1/2019 150 D -25 10
101 4/1/2019 75 D -100 10
101 4/1/2019 3 D -103 0
101 4/1/2019 75 D -178 0
101 4/2/2019 100 C -198 -98 0
101 4/2/2019 125 D -223 10
101 4/2/2019 150 D -373 10
102 4/1/2019 50 C 125 175 0
102 4/1/2019 125 C 300 0
102 4/2/2019 250 D 50 0
102 4/2/2019 10 D 40 0

Answer 1

A few tips:
You have the same code for incrementing act_bal in both the if and else blocks, so factor it out. Don't repeat yourself.
You can skip the retain statement if you use a sum statement.
Use a separate variable to keep track of the number of penalties triggered per day, but only apply the first two of them.
So, putting it all together:
data want;
set have;
by id date;
if first.date and not first.id then op_bal = act_bal;
if first.date then do;
act_bal = op_bal;
penalties = 0;
end;
if type='C' then act_bal + amount;
if type='D' then act_bal + (-amount);
if amount > 4 and type='D' then penalties + 1;
if last.date then act_bal + (-min(penalties,2) * 10);
run;