Replace a row value with previous by group in SAS - sas

Question

Is there a way I could replace a row value to its previous row by each group?
Below is the before and after data set. Product for each type - C needs to be changed as type - L for each customer when the ID is same it has the highest amount.
Before
ObsCust LINK_ID Type Product Amount
1 1 12432 L A 23
2 1 12432 C B 0
3 2 23213 L C 234
4 2 23145 L D 25
5 2 23145 C E 0
6 3 21311 L F 34
7 3 21324 L G 45
8 3 21324 L H 35
9 3 21324 C I 0
After
Cust LINK_ID Type Product Amount
1 12432 L A                234
1 12432 C A                   -  
2 23213 L C           23,212
2 23145 L D                335
2 23145 C D                   -  
3 21311 L F                323
3 21324 L G             2,344
3 21324 L H                  34
3 21324 C G                   -  
Thank you!

Answer 1

if i understand correctly, you want to have product value for C Type be the product associated with the highest amount in L Types. If this is correct one possible way is to use the following. First the product with the highest amount for L-Type within each group of customers and IDs are calculated as follows:
note that the original dataset is assumed to be named "example".
proc sql;
create table L_Type as
select cust, LINK_ID, product, amount
from example
where type = 'L' and amount = max(amount)
group by cust, LINK_ID
;
quit;
then product calculated above is coded for c type in the original example.
proc sql;
select
e.cust
, e.LINK_ID
, e.type
, case when e.type = 'C' then b.product end as product
, e.amount
from example e left join L_Type b
on e.cust = b.cust and e.LINK_ID = b.LINK_ID
;
quit;

Answer 2

So you have a couple processing tasks to do:
Have you considered all the edge cases ?
For a customer find the row(s) with the maximum amount.
Is one of them type L ?
No, do nothing
Yes, track the Product and LinkId as follows
Is there more than one 'maximal' row ?
No, track the Product & LinkId from the one row
Yes, Is there more than one Product in the rows ?
No, track the Product value
Is there more than one LinkId ?
No, track the LinkId
Yes, Which LinkIds?
Track all the different LinkIds
Track one of these: first, lowest, highest, last LinkId
Yes, now what ?
Log an error ?
Track one of the Product values because only one can be used, which one ?
first occurring ?
lowest value ?
highest value ?
last occurring ?
For the tracked LinkIds (there might not be any) apply the tracked Product to the rows that are type C (or perhaps type not L)