topic Re: How to implement nested loop structures in SAS Procedures

How to implement nested loop structures

Mikeyjh — Wed, 05 Dec 2012 22:06:38 GMT

Hi all,

I would like to implement a 2 level nested loop in SAS. Please see SAS pseudo code below.

I have a list of subject numbers held in the dataset "subjects" and a list of dataset names held in dataset "datatypes". Each of the datatypes referenced by the dataset "datatypes" would be an individual dataset.

Data _null_;

set subjects;

pt = subjid;

Data _null_;

set datatypes;

dt = datatype;

* print all the data for the current pt and dt, eg, "select * from dt where subjid = pt"

Run;

Please note that its the code for the 2 level nested loop that I need and not the how to implement the specific code within the loops.

Thanks for your help.

Re: How to implement nested loop structures

PGStats — Wed, 05 Dec 2012 22:54:44 GMT

I think it can be done this way, using a single MACRO variable (untested) :

proc sql;

select distinct dataType into :inCmd separated by " " from datatypes;

quit;

data allDatatypes;

set &inCmd indsname=dataType;

run;

proc sql;

select S.subjId as pt, D.dataType as dt, /* and whatever you need */

from subjects as S inner join allDataTypes as D on S.subjId=D.subjId;

drop allDataTypes;

quit;

Re: How to implement nested loop structures

Mikeyjh — Wed, 05 Dec 2012 23:46:27 GMT

Thanks for your reply PG.

Can you explain what your allDataTypes statement does especially the "indsname=dataType"?

Re: How to implement nested loop structures

Tom — Wed, 05 Dec 2012 23:50:08 GMT

Why do you feel the need to nest it?

Sounds like you want to make a patient profile report.

One way is to create a macro that reports one patient then generate a call to the macro for each patient.

%macro patprofile(ptid);

%local dslist ds i ;

%let dslist = dm ae ;

%do i=1 %to %sysfunc(countw(&dslist));

%let ds=%scan(&dslist,&it);

proc print data=&ds ;

where ptid=&ptid;

run;

%end;

%mend patprofile;

filename code temp;

data _null_;

set patlist;

put '%patprofile(' ptid ');';

run;

%inc code / source2 ;

Re: How to implement nested loop structures

Astounding — Wed, 05 Dec 2012 23:53:48 GMT

It's not clear how general this needs to be, but here's another approach.

data _null_;

set datatypes;

call execute('data ' || strip(datatype) || '; set subjects; run;');

run;

If the requirements become really involved, this might get cumbersome. But it might do the job that you require. Here's another thought as well that begins the same as PGStats' suggestion:

proc sql noprint;

select distinct strip(datatype) into : dataset_list separated by ' ' from datatypes

quit;

data &dataset_list;

set subjects;

run;

Of course, this doesn't work if you need a more involved analysis, such as a PROC FREQ for each data set. But if that might be needed, there are definitely ways to loop through each data set name in a list. See how close you come to what you need with this much, and we can always embellish later.

Good luck.

Re: How to implement nested loop structures

PGStats — Thu, 06 Dec 2012 00:48:27 GMT

The first step creates a list of the dataset names.

The second step reads and concatenates all those datasets in the list and creates a new variable called dataType to keep the name of the dataset that contributed each observation.

The third step is a query that joins the Subjects dataset with the allDataTypes dataset by pairing observations with the same subjId.

Hth.