topic Re: Loop in Macro in SAS Programming

Loop in Macro

Ujjawal — Sun, 12 Apr 2015 09:23:04 GMT

Hi SAS Experts -

I have a macro that calculates acceptable range of a variable. An acceptable range is defined by :

Lower Limit = Q1 - 1.5*(Q3-Q1)

Upper Limit = Q3 + 1.5*(Q3-Q1)

It's a boxplot method of calculating outliers. The macro is working fine. But it is inefficient in terms of its processing as it calculates outliers for each variable in a loop and then capping values. I want proc univariate to be run for all the variables (not in loop) and save output in a dataset and then capping for variables using IF THEN at one time only.

Code : -

options mprint symbolgen;

%macro outliers(input=, vars=, output= );

data &output;

set &input;

run;

%let n=%sysfunc(countw(&vars));

%do i= 1 %to &n;

%let val = %scan(&vars,&i);

/* Calculate the quartiles and inter-quartile range using proc univariate */

proc univariate data=&output noprint;

var &val;

output out=temp QRANGE= IQR Q1= First_Qtl Q3= Third_Qtl;

run;

/* Extract the upper and lower limits into macro variables */

data _null_;

set temp;

call symput('QR', IQR);

call symput('Q1', First_Qtl);

call symput('Q3', Third_Qtl);

run;

%let ULimit=%sysevalf(&Q3 + 1.5 * &QR);

%let LLimit=%sysevalf(&Q1 - 1.5 * &QR);

/* Final dataset excluding outliers*/

data &output;

set &output;

if &val < &Llimit then &val = &Llimit;

if &val > &Ulimit then &val = &Ulimit;

run;

%end;

%mend;

%outliers(Input=abcd, Vars = a, output= test);

Thanks in anticipation!

Re: Loop in Macro

Jagadishkatam — Sun, 12 Apr 2015 13:58:33 GMT

If we are using univariate we could calculate the statistics of only one variable at a time. So the method you are following is correct.

Re: Loop in Macro

jakarman — Sun, 12 Apr 2015 15:36:49 GMT

SAS procs are designed to handle a lot of variables in one run on the data.

Even the outputdataset of Univariate Base SAS(R) 9.4 Procedures Guide: Statistical Procedures, Second Edition It ends with mentioning two variables being processed each getting different suffixes.

You are starting your question with "you are having a macro" There could be a confusion there.

Macro-s in SAS are source text base ones (type 2) and not functional processes (type 3) or recorded keyboard/mouse actions (type 1). If you are trying to use macro-s as you used that with that word in Excel or any other programming language leave that behind you and program your logic understanding SAS from scratch http://en.wikipedia.org/wiki/Macro_(computer_science)

Just another question as you are trying to build boxplots http://nesug.org/proceedings/nesug08/np/np16.pdf

Did you check whether your question is easily solved by the many procs (modern word would be now packages) that are around .

Re: Loop in Macro

Reeza — Sun, 12 Apr 2015 16:29:56 GMT

For part 1 switch to proc means. I don't think you need a macro for this at all, but perhaps Jaap's paper has illustrated it better than I can here.

Here's two different ways of generating the stats for all variables at once:

proc means data=sashelp.class stackods n p25 p75 qrange median;

var age weight height;

ods output summary=want1;

output out=want2 n= p25= p75= qrange= median=/autoname;

run;