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Understanding macro variables in SAS

Why do we need macro variables

Macro variables allow values to be defined once and reused throughout a program
This makes code more dynamic and easier to maintain
If a date, period, dataset name, or label changes, we can update one macro variable instead of editing many lines of code
Macro variables are one of the main tools SAS provides for code automation

Concept	Definition
Macro variable	A macro variable stores text that can be substituted into SAS code dynamically.
User defined macro variable	A macro variable created by the programmer to store a custom value.
System defined macro variable	A macro variable automatically provided by SAS to hold environment information such as date, time, or user id.

Create sample data

These datasets will be used in the examples that follow
The data is intentionally small, so the effect of macro variable substitution is easy to see

data sales_data;
    input sale_date :date9. amount department $;
    format sale_date date9.;
    datalines;
01JAN2024 1000 Marketing
01JAN2024 1500 Sales
02JAN2024 2000 Marketing
02JAN2024 1800 Sales
;
run;
 
data department_sales;
    input department $ sales;
    datalines;
Marketing 15000
Sales 20000
;
run;
 
data all_sales;
    input sale_date :date9. amount;
    format sale_date date9.;
    datalines;
01JAN2020 500
02JAN2020 700
01JAN2021 800
02JAN2021 900
01JAN2022 1000
02JAN2022 1100
01JAN2023 1200
02JAN2023 1300
;
run;

Create and use a user defined macro variable

The `%let` statement creates a macro variable and assigns text to it
We reference a macro variable by prefixing its name with an ampersand
Here, the macro variable `report_date` is used in both a WHERE condition and a report title

%let report_date=01JAN2024;
 
data sales_summary;
    set sales_data;
    where sale_date="&report_date"d;
run;
 
proc print data=sales_summary;
    title "Sales Summary for &report_date";
run;

The same value `01JAN2024` is reused in multiple places through one macro variable
If the report date changes, only the `%let` statement needs to be updated

Examples of system defined macro variables

SAS automatically provides many useful macro variables
Examples include `&SYSDATE`, `&SYSTIME`, and `&SYSUSERID`
These values are often used in titles, logs, file names, and audit-style outputs

data log_details;
    log_date="&SYSDATE"d;
    log_time="&SYSTIME";
    user_id="&SYSUSERID";
    format log_date date9.;
run;
 
proc print data=log_details;
    title "Log Details for &SYSUSERID on &SYSDATE";
run;

Inspect `log_details` and confirm that the values reflect the current SAS session environment

Use macro variables in titles and labels

Macro variables are not limited to data filtering
They can also be used in titles, labels, file names, and many other places where SAS expects text

%let department=Marketing;
 
proc print data=department_sales;
    title "Sales Report for &department Department";
    label sales="Total Sales in &department";
run;

The title and label are customised dynamically using the same macro variable value

Use macro variables with iterative processing

Macro variables are commonly used together with SAS macros to repeat code for multiple values
In this example, a report is created for each year from 2020 to 2023
The loop variable `year` behaves like a macro variable inside the macro definition

%macro generate_reports;
    %do year=2020 %to 2023;
        data sales_&year;
            set all_sales;
            where year(sale_date)=&year;
        run;
 
        proc print data=sales_&year;
            title "Sales Report for &year";
        run;
    %end;
%mend generate_reports;
 
%generate_reports;

The macro creates four datasets named `sales_2020` through `sales_2023`
This demonstrates how macro variables help generate repeated code patterns automatically

Key points to remember

Macro variables store text, not SAS data values in a dataset
User defined macro variables are usually created with `%let`
System macro variables are provided automatically by SAS
Macro variables help with dynamic code, reusable code, and automation

*Copyright @ www.mycsg.in;

Understanding macro variables in SAS

Why do we need macro variables

Create sample data

SAS Log

Dataset View

Create and use a user defined macro variable

SAS Log

Dataset View

Examples of system defined macro variables

SAS Log

Dataset View

Use macro variables in titles and labels

SAS Log

Use macro variables with iterative processing

SAS Log

Dataset View

Key points to remember