topic why does do while retain values from if then. in SAS Programming

why does do while retain values from if then.

rudfaden — Mon, 18 Sep 2017 11:14:14 GMT

Can anybody give me the explanation to why the values nn2 and n3 are retained in this do while statement?

data test;
n=0;
   do while(n<5);
      put n=;
      n+1;
	  if n=1 then n2=1;
	  if n=2 then n3=2;
	  output;
	end;
run;

Re: why does do while retain values from if then.

WarrenKuhfeld — Mon, 18 Sep 2017 12:04:30 GMT

You have a one pass data step. It never goes back for a second pass becasue there is not input data set. Nothing is retained (in the normal SAS sense). Nothing is reinitialized to missing for the second pass, because there is no second pass.

Re: why does do while retain values from if then.

gamotte — Mon, 18 Sep 2017 12:07:13 GMT

Hello,

The PDV, that is, the vector holding values for the currently processed observation is only cleared

when the interpreter meets the run instruction. Here, you are always processing the same observation that

you modify and output several times. There is no reason for the values of n2 and n3 to be reset.

Re: why does do while retain values from if then.

rudfaden — Mon, 18 Sep 2017 12:07:48 GMT

Are you saying it is because sas keeps n2 and n3 in memory and then keeps priting the same values?

Re: why does do while retain values from if then.

ballardw — Mon, 18 Sep 2017 17:34:02 GMT

Maybe this adds a bit to what goes on:

data test;
n=0;
   do while(n<5);
      put n=;
      n+1;
	  if n=1 then n2=1;
          else n2=.;
	  if n=2 then n3=2;
          else n3=.;
	  output;
	end;
run;