topic Re: Help with macro loop in New SAS User

Help with macro loop

polpel — Thu, 10 Oct 2019 13:20:23 GMT

Hello,

I was wondering if someone could explain this loop for me please, and if it's well indented and stuff.

put "loop start";
     %do j=1 %to 9 ;
          %let k=%eval(&j-1);
          put "boucle j=&j, k=&k";       
          if surv&k>0 and surv&j=0 
          then do;
                surv&j=datesurv; 
                put "loop end";
          end;
          else do;
     %end;
     %do j=1 %to 9 ;
          end;
     %end;

Thanks a lot

Re: Help with macro loop

Tom — Thu, 10 Oct 2019 13:30:53 GMT

You want style feedback?

The first PUT statement is wrong. The generated SAS code does not have any loops. It is just 9 nested IF/THEN statements.

The other PUT statements also don't make much sense. Are you trying to see which IF statements are being evaluated for every observation? Why not just store that information into another variable instead?

If you want functionality feedback provide explanation of what the code is trying to do and provide input data and expected output.

Re: Help with macro loop

Kurt_Bremser — Thu, 10 Oct 2019 13:38:34 GMT

Almost classic abuse of the macro language for data manipulation. The poor creature who came up with this should have all memory of macros removed from their brains, so that there will be enough space to learn how to use Base SAS properly:

array surv[0:9] surv0-surv9;
do j = 1 to 9;
  if surv[j-1] > 0 and surv[j] = 0
  then do;
    surv[j] = datesurv;
    j=10;
  end;
end;

Re: Help with macro loop

polpel — Thu, 17 Oct 2019 12:08:37 GMT

The person who wrote that code explained it to me and it actually makes a lot of sense.

He cleverly used macro language to actually write SAS code which is how you should be using macro language.

Re: Help with macro loop

Patrick — Thu, 17 Oct 2019 12:20:38 GMT

@polpel wrote:

The person who wrote that code explained it to me and it actually makes a lot of sense.

He cleverly used macro language to actually write SAS code which is how you should be using macro language.

Yes, that's what one uses SAS macro language mostly for: To dynamically create SAS code. BUT: The rule of thumb is to only use macro language if you can't do it with normal SAS language - and this is not the case here.

Compare the macro code you've posted with the Base SAS language alternative @Kurt_Bremser proposes. What do you think is easier to understand, maintain and debug?

Re: Help with macro loop

polpel — Thu, 17 Oct 2019 12:32:10 GMT

Okay yes I see. Thanks again for all the help and explanations!

Re: Help with macro loop

mjizzle — Wed, 20 Nov 2019 17:58:26 GMT

I have two sets of column names in my database such as columnA_1, columnA_2 ... all the way till 17. And another column name like columnB_1, columnB_2... all the way to 9. I want to create a new variable that checks if these columns have same values (character) and how many of them have same values. For Example consider the following table:

A_1 A_2 A_3 A_4 B_1 B_2 B_3 B_4

John Adam David Sam Adam John Matt Tom

In the above data, I want the code to check all the columns from A_X with values of columns in B_X and give me a number = 2. i.e Adam and John is common between them. This is the code I am trying but is not working at all. I am not an expert in SAS so I am learning by doing but am unsuccessful so far. Any help is appreciated.


%macro create(adv);
data nestedcommon2;
set nestedcommon1;
%do i=1 %to 17;
%do j= 1 %to 9;
common=0;
%if acq_adv_&i=tar_adv_&j %then common =  common+1;
%end;
%end;
 final=common;
run;
%mend create;
%create(153)

Thanks,

Mjizzle

Re: Help with macro loop

PaigeMiller — Wed, 20 Nov 2019 18:25:05 GMT

@mjizzle wrote:
 
I have two sets of column names in my database such as columnA_1, columnA_2 ... all the way till 17. And another column name like columnB_1, columnB_2... all the way to 9. I want to create a new variable that checks if these columns have same values (character) and how many of them have same values. For Example consider the following table:

A_1 A_2 A_3 A_4 B_1 B_2 B_3 B_4

John Adam David Sam Adam John Matt Tom

In the above data, I want the code to check all the columns from A_X with values of columns in B_X and give me a number = 2. i.e Adam and John is common between them. This is the code I am trying but is not working at all. I am not an expert in SAS so I am learning by doing but am unsuccessful so far. Any help is appreciated.
%macro create(adv);
data nestedcommon2;
set nestedcommon1;
%do i=1 %to 17;
%do j= 1 %to 9;
common=0;
%if acq_adv_&i=tar_adv_&j %then common =  common+1;
%end;
%end;
 final=common;
run;
%mend create;
%create(153)

As stated above to the original poster, get rid of macros and macro variables here. They are a completely unnecessary (and in this case ineffective) way to accomplish the goal. Learn to use data steps and the power of data steps.

Specifically, use ARRAYs when you are in a data step and want to perform tasks across multiple variables in the same observation.

For example:

/* Untested Code */

data nestedcommon2;
    set nestedcommon1;
    array acq_adv acq_adv1-acq_adv17;
    array tar_adv tar_adv1-tar_adv9;
    common=0;
    do i=1 to 17;
        do j=1 to 9;
             if acq_adv(i)=tar-adv(j) then common=common+1;
        and;
    end;
run;

Re: Help with macro loop

mjizzle — Wed, 20 Nov 2019 22:36:38 GMT

Perfect! Thank you so much for your quick reply.

Best,

Mjizzle