CODEWITHSUNDEEP
sas
navkast
navkast

Reputation: 468

How do I create a SAS variable that depends on itself?

I have a dataset (see picture below). I need to fill the stitched_price column. For row 1, I need to use the value from 'price.' This works.

For row 2 onwards, I need to do the following: stitched_price = lag(stitched_price) * (trade_return + 1). However, this doesn't work and leaves all rows > 1 blank.

Here is my code:

data test2;
    set test;
    if _N_ = 1 then stitched_price = price;
    else stitched_price = lag(stitched_price) * (1 + trade_return);
run;

I am not sure why this is happening. I understand that there are intricacies involved with using lag in an if statement, but is there a way around this?

This is the result of the code. Prior to running the code, everything is the same except for the absence of the stitched_price variable.

Upvotes: 0

Views: 372

Answers (1)

Reeza
Reeza

Reputation: 21264

Try retain instead:

data test2;
   set test;
    retain stitched_price;
    if _N_ = 1 then stitched_price = price;
    else stitched_price = stitched_price * (1 + trade_return);
run;

In general lag doesn't work in conditional blocks. If you did want to use lag, it would be something like follows:

data test2;
   set test;
    lag_s=lag(stitched_price);
    if _N_ = 1 then stitched_price = price;
    else stitched_price = lag_s * (1 + trade_return);
run;

Here's an older post on why lag doesn't work and I'm sure Google has many others: lag function doesn't work in SAS

Upvotes: 2

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