topic Re: New variable length in SAS Programming

New variable length

Ronein — Sun, 07 May 2023 04:22:26 GMT

Hello

What is the reason that in data set "Have2" the new variable X_new have length 1 and not 3 as in the original variable?

data have;
input X $;
cards;
MAX
MAX
VISA
DINERS
MAX
;
Run;

data have2 ;
set have;
IF _n_<=2 then X_new='';else X_new=X;
Run;

Re: New variable length

Kurt_Bremser — Sun, 07 May 2023 04:54:56 GMT

Because in the first occurence in your code you give it a length of 1:

IF _n_<=2 then X_new='';else X_new=X;

The data step compiler takes the length from this first occurence to define the variable in the PDV.

Bottom line: to set a length for a variable, always use one of the explicit methods (LENGTH or ATTRIB statement) instead of implicit methods like you did here.

Re: New variable length

Ronein — Sun, 07 May 2023 20:48:45 GMT

So better always to define length of a new variable and not let SAS decide for me....

Re: New variable length

Tom — Sun, 07 May 2023 20:58:40 GMT

@Ronein wrote:
So better always to define length of a new variable and not let SAS decide for me....

If you KNOW the length it should have then yes be explicit. The programmer that has to fix your code (which is usually you) will appreciate it.

If you want to make the code mimic an existing variable then you could easily re-write your logic so the compiler sees the simple copy of the old variable as the first place the new variable is referenced.

data have2 ;
  set have;
  X_new=X;
  if _n_<=2 then X_new=' ';
run;

And if you use CALL MISSING() it will work whether X is numeric or character.

data have2 ;
  set have;
  X_new=X;
  if _n_<=2 then call missing(X_new);
run;

If you want it to inherit the format, label and other attributes then you could get even trickier.

data have2 ;
  set have;
  set have(keep=x rename=(x=X_new));
  if _n_<=2 then call missing(X_new);
run;

Re: New variable length

Kurt_Bremser — Mon, 08 May 2023 03:40:19 GMT

@Ronein wrote:
So better always to define length of a new variable and not let SAS decide for me....

aka Maxim 47.