topic Re: Creating variable based on prior value within repeated tests in SAS Programming

Creating variable based on prior value within repeated tests

jmarnaez — Tue, 28 Jun 2022 03:34:58 GMT

Sorry if the title isn't quite accurate, but it's the most succinct way I could think. I have a large dataset in which some individuals have multiple tests (each individual is given a unique ID). Some of my team members are interested in identifying time to follow up on elevated tests and I'm not quite sure how to do that in SAS. Functionally I need to create a variable that indicates whether the previous test for that ID was elevated in cases where an ID has multiple tests on different dates. Any help with this would be greatly appreciated.

Re: Creating variable based on prior value within repeated tests

mkeintz — Tue, 28 Jun 2022 03:40:14 GMT

Please show some sample data, in the form of a working data step.

And the corresponding desired output.

Help us help you.

Re: Creating variable based on prior value within repeated tests

jmarnaez — Tue, 28 Jun 2022 04:21:21 GMT

I do not have access to SAS right now to test the data step, I'll provide what some truncated data looks like and what I'd like the end product to be.

data test;

input ID TestDate Elevated $;

datalines;

1 20200101 Y

1 20200105 N

1 20200110 N

2 20200106 Y

2 20200108 N

3 20200112 Y

3 20200114 Y

3 20200125 Y;

run;

ID TestDate Elevated

1 20200101 Y

1 20200105 N

1 20200110 N

2 20200106 Y

2 20200108 N

3 20200112 Y

3 20200114 Y

3 20200125 Y

What I'd like the data to look like with the new variable is this

ID TestDate Elevated Prior Elevated

1 20200101 Y NA

1 20200105 N Y

1 20200110 N N

2 20200106 Y NA

2 20200108 N Y

3 20200112 Y NA

3 20200114 Y Y

3 20200125 Y Y

Re: Creating variable based on prior value within repeated tests

andreas_lds — Tue, 28 Jun 2022 06:07:05 GMT

Something like

data want;
   set test;
   by Id;
   
   prior_elevated = lag(Elevated);
   
   if first.id then prior_elevated = ' ';
run;

should do it.

Re: Creating variable based on prior value within repeated tests

mkeintz — Wed, 29 Jun 2022 04:36:49 GMT

Thanks for posting sample data.

The response by @andreas_lds will certainly produce your sample output.

But how does your sample output provide "time to follow up on elevated tests" which you described as your teammates' interest in your original post?