You can use the LAG function in SAS to retrieve lagged values of some variable.

This function uses the following basic syntax:

lag1_value = lag(value);

By default, lag finds the previous value of some variable.

However, you can use lag2, lag3, lagn, etc. to calculate the 2-lagged, 3-lagged, n-lagged, etc. values of some variable.

The following examples show how to use the lag function in practice.

Example 1: Calculated Lagged Values for Some Variable

Suppose we have the following dataset in SAS that shows the total sales made by some store on consecutive days:

/*create dataset*/
data original_data;
    input day $ sales;
    datalines;
1 14
2 19
3 22
4 20
5 16
6 26
7 40
8 43
9 29
10 30
11 35
12 33
;
run;/*view dataset*/
proc printdata=my_data;

The following code shows how to calculate the value for sales lagged by 1, 2, and 3 days:

/*create new dataset that shows lagged values of sales*/
data new_data;
    set original_data;
    lag1_sales = lag(sales);
    lag2_sales = lag2(sales);
    lag3_sales = lag3(sales);
run;

/*view new dataset*/
proc printdata=new_data;

The three new columns (lag1_sales, lag2_sales, lag3_sales) show the sales lagged by one, two, and three days, respectively.

Example 2: Calculated Lagged Values by Group

Suppose we have the following dataset in SAS that shows the total sales made by two stores during consecutive days:

/*create dataset*/
data original_data;
    input store $ sales;
    datalines;
A 14
A 19
A 22
A 20
A 16
A 26
B 40
B 43
B 29
B 30
B 35
B 33
;
run;

/*view dataset*/
proc printdata=original_data;

We can use the following code to calculate the 1-day lagged sales values by store:

/*create new dataset that shows lagged values of sales by store*/
data new_data;
	set original_data;
	by store;
	lag1_sales = lag(sales);
	if first.store then lag1_sales = .;
run;

/*view new dataset*/
proc printdata=new_data;

The values in the lag1_sales column show the 1-day lagged sales values for each store.

Notice that the value for lag1_sales in row 7 is empty because the 1-day lagged value for that row represents a sales value for a different store.

Additional Resources

The following tutorials explain how to perform other common tasks in SAS: