I know that SAS can do this with PROC LIFETEST, but I want to attempt this by hand. Even though I can easily do this in Excel or R, this might be a good learning experience. I am essentially trying to reproduce the product-limit table for some survival data. Below is a look at how my data currently looks. The value in "AtRisk" is a macro variable placed in the dataset if it is the first observation.
What I want to do is calculate AtRisk(i) = AtRisk(i-1)-censored(i-1)-event(i-1). In other words, AtRisk for SurvivalTime=2 is 49-5-0=44. Then At Risk for SurvivalTime=2 is 44-0-1=43, etc.
I have tried using the RETAIN statement and the lag() function to perform this, but I cannot get either one to work. If you have any better ideas, please help me out!
Here is an example of my code that does not do the trick:
data data2;
set data1;
by _LABEL_; /* NOTE: _LABEL_ has the same value throughout the data */
if first._LABEL_ then atrisk=&atrisk.;
else atrisk=lag(atrisk);
run;
CURRENT DATA:
_NAME_ | SurvivalTime | Censorred | Event | AtRisk |
---|---|---|---|---|
COUNT | 1 | 5 | 0 | 49 |
COUNT | 2 | 0 | 1 | . |
COUNT | 3 | 0 | 1 | . |
COUNT | 4 | 1 | 0 | . |
COUNT | 5 | 0 | 1 | . |
... | ... | ... | ... | ... |
CORRECT DATA:
SurvivalTime | Censored | Event | AtRisk |
---|---|---|---|
1 | 5 | 0 | 49 |
2 | 0 | 1 | 44 |
3 | 0 | 1 | 43 |
4 | 1 | 0 | 42 |
5 | 0 | 1 | 41 |
... | ... | ... | ... |
%let AtRisk=49;
data want (drop=Last:);
input _NAME_ $ SurvivalTime Censorred Event;
retain AtRisk LastAtRisk;
AtRisk=ifn(_n_ eq 1,&AtRisk,
LastAtRisk);
LastAtRisk=AtRisk-Censorred-Event;
cards;
COUNT 1 5 0
COUNT 2 0 1
COUNT 3 0 1
COUNT 4 1 0
COUNT 5 0 1
;
How about this?
data data2;
set data1;
retain atrisk;
if _n_ = 1 then atrisk = &atrisk;
else atrisk = atrisk - censored - lag( event );
run;
%let AtRisk=49;
data want (drop=Last:);
input _NAME_ $ SurvivalTime Censorred Event;
retain AtRisk LastAtRisk;
AtRisk=ifn(_n_ eq 1,&AtRisk,
LastAtRisk);
LastAtRisk=AtRisk-Censorred-Event;
cards;
COUNT 1 5 0
COUNT 2 0 1
COUNT 3 0 1
COUNT 4 1 0
COUNT 5 0 1
;
Build your skills. Make connections. Enjoy creative freedom. Maybe change the world. Registration is now open through August 30th. Visit the SAS Hackathon homepage.
Register today!Learn how use the CAT functions in SAS to join values from multiple variables into a single value.
Find more tutorials on the SAS Users YouTube channel.
Select SAS Training centers are offering in-person courses. View upcoming courses for: