how to add a new variable into an existing dataset using metadata function

[alepage]

Hello,

I would like to know if there is a way to add a new variable to an existing dataset without creating the updated dataset (i,e, the existing dataset with the new variable added).

I would like to know if there is a way add a new variable but without having to create the dataset
see code below:

%macro VarExist(dsn=,varname=);
%let dsn2=&dsn.;
%local dsid vnum;
%let vnum=0;
%let dsid = %sysfunc(open(&dsn));
%if &dsid %then %do;
 %let vnum = %sysfunc(varnum(&dsid,&varname));
 %let dsid = %sysfunc(close(&dsid));
%end;
&vnum
%mend ;

data test;
set sashelp.class;
run;

%if %varexist(dsn=test,varname= New_Variable ) = 0 %then 
	%do;
		data &dsn2.;
		%put &=dsn2.;
		attrib New_Variable	label="New Variable" 	length=$5. 	format=$5. 	informat=$5.;
		set &dsn2.;
		run;
	%end;

[Quentin]

Can you describe your question a bit more?

If you want to add a variable to an existing dataset, then by definition that dataset will be updated (actually over-written) when you add a variable to it.

[alepage]

in the SAS code,  more precisely at the if condition,

I am using an attribute statement with a set statement to update the dataset as below.

%if %varexist(dsn=test,varname= New_Variable ) = 0 %then 
	%do;
		data &dsn2.;
		%put &=dsn2.;
		attrib New_Variable	label="New Variable" 	length=$5. 	format=$5. 	informat=$5.;
		set &dsn2.;
		run;
	%end;

I wonder if it could be possible to add  a new variable  with the dataset identifier

as below and if so, how do we do that.

%let dsid = %sysfunc(open(&dsn));
%if &dsid %then %do;
adding the new variable with its name, label and format.
 %let dsid = %sysfunc(close(&dsid));

[Quentin]

Ahh, I see.  It's always risky to say "no" when someone asks if it's possible to do something in SAS, but I don't think you can use the metadata functions for adding variables.  In order to add a variable to a dataset, SAS has to rewrite the dataset (header metadata and data).  That is a job for the DATA step.

If by tiny chance your goal is to write a function-style macro that would add variables to a dataset, that would be possible (using DOSUBL) but it would still use a DATA step.

[Kurt_Bremser · Accepted solution]

Adding a variable changes the observation length; since observations always occupy a contiguous space, the dataset needs to be rewritten.

[SASKiwi]

As @Kurt_Bremser has stated, anytime you add or drop columns from a SAS dataset, you need to add or remove the space to hold it even if it contains only missing values. Changing just the descriptor portion of a SAS dataset is not possible when it involves adding or dropping columns.