How to Use FIRST. and LAST. Variables in SAS

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You can use the FIRST. and LAST. functions in SAS to identify the first and last observations by group in a SAS dataset.

Here is what each function does in a nutshell:

• FIRST.variable_name assigns a value of 1 to the first observation in a group and a value of 0 to every other observation in the group.
• LAST.variable_name assigns a value of 1 to the last observation in a group and a value of 0 to every other observation in the group.

The following examples show how to use each function in practice with the following dataset in SAS:

/*create dataset*/
data my_data;
    input team $ points rebounds;
    datalines;
Mavs 29 10
Mavs 13 6
Mavs 22 5
Mavs 20 9
Spurs 13 9
Spurs 15 10
Spurs 33 8
Spurs 27 11
Rockets 25 8
Rockets 14 4
Rockets 16 7
Rockets 12 4
;
run;

/*view dataset*/
proc print data=my_data;

Example 1: How to Use FIRST. in SAS

We can use the following FIRST. function in SAS to assign a value of 1 to the first observation for each team in the dataset:

/*sort dataset by team*/
proc sort data=my_data;
    by team;
run;

/*create new dataset that labels first row for each team*/
data first_team;
    set my_data;
    by team;
    first_team=first.team;
run;

/*view dataset*/
proc print data=first_team;

Notice that the first_team column assigns the first observation for each team a value of 1. All other values are assigned a value of 0.

You can also use the following code to create a new dataset that only contains the first observation for each team:

/*sort dataset by team*/
proc sort data=my_data;
    by team;
run;

/*create new dataset only contains first row for each team*/
data first_team;
    set my_data;
    by team;
    if first.team;
run;

/*view dataset*/
proc print data=first_team;

Notice that the dataset only contains the first observation for each team.

Example 2: How to Use LAST. in SAS

We can use the following LAST. function in SAS to assign a value of 1 to the first observation for each team in the dataset:

/*sort dataset by team*/
proc sort data=my_data;
    by team;
run;

/*create new dataset that labels last row for each team*/
data last_team;
    set my_data;
    by team;
    last_team=last.team;
run;

/*view dataset*/
proc print data=last_team;

Notice that the last_team column assigns the last observation for each team a value of 1. All other values are assigned a value of 0.

You can also use the following code to create a new dataset that only contains the last observation for each team:

/*sort dataset by team*/
proc sort data=my_data;
    by team;
run;

/*create new dataset only contains last row for each team*/
data last_team;
    set my_data;
    by team;
    if last.team;
run;

/*view dataset*/
proc print data=last_team;

Notice that the dataset only contains the last observation for each team.

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