Finding the max date across different variables to create a new variable

[fordcr2]

Hello, 

I need to create a variable (withdrawal_date) based off of the maximum date value for each participant id. I put in some fake data into this dataset to test some SAS codes to find a way to give me the maximum value across multiple variables, and then I need to make that value be the value of the created withdrawal_date variable. I found a macro to output the maximum variable, but it just gives me the variable name that has the max value. I am trying to figure out a way to code it so that the maximum value (not variable name) is output as the new variable. 

Raw "fake" data:

id session1 session2 session3 session4

1	01/23/2019	02/01/2019	04/05/2019	06/01/2019
2	05/25/2019	07/02/2019	.	.
3	04/07/2019	06/07/2019	09/09/2019	.
4	10/02/2019	10/28/2019	11/05/2019	.
5	03/04/2019	.	.	.
6	06/07/2019	07/04/2019	08/17/2019	10/01/2019
7	03/06/2019	03/27/2019	.	.

Macro: 

%macro test(dsn,vars,func);
data new;
set &dsn;
array list(*) &vars;
&func = vname(list[whichn(&func(of list[*]), of list[*])]);
run;
%mend test;

/** retrieve maximum value from a b and c **/
%test(fake,session1 session2 session3 session4 session5,max)

proc print;
run;

/** retrieve maximum value from all numeric variables **/
%test(fake,_numeric_,max)

proc print;
run;

Output from macro:

id  session1 session2 session3 session4 max

1	01/23/2019	02/01/2019	04/05/2019	06/01/2019	session4
2	05/25/2019	07/02/2019	.	.	session2
3	04/07/2019	06/07/2019	09/09/2019	.	session3
4	10/02/2019	10/28/2019	11/05/2019	.	session3
5	03/04/2019	.	.	.	session1
6	06/07/2019	07/04/2019	08/17/2019	10/01/2019	session4
7	03/06/2019	03/27/2019	.	.	session2

Desired output:

id session1 session2 session3 session4 withdrawal_date

1	01/23/2019	02/01/2019	04/05/2019	06/01/2019	06/01/2019
2	05/25/2019	07/02/2019	.	.	07/02/2019
3	04/07/2019	06/07/2019	09/09/2019	.	09/09/2019
4	10/02/2019	10/28/2019	11/05/2019	.	11/05/2019
5	03/04/2019	.	.	.	03/04/2019
6	06/07/2019	07/04/2019	08/17/2019	10/01/2019	10/01/2019
7	03/06/2019	03/27/2019	.	.	03/27/2019

Thanks in advance!

[Reeza · Accepted solution]

withdrawal_date = max(of session1-session4);

That's all you should need. No macro needed anywhere.

[fordcr2]

Well that was easy  Thank you!!