A DO loop in SAS can be used to do some action a certain number of times.

There are three basic DO loops in SAS:

1. DO Loop

data data1;
x = 0;
do i = 1 to 10;
   x = i*4;
   output;
end;
run;

What It Does: This loop performs 10 iterations, from i = 1 to 10, where the value in each row is equal to i multiplied by 4.

When It Stops: This loop only stops after 10 iterations have been performed.

2. DO WHILE Loop

data data2;
x = 0;
do i = 1 to 10 while(x < 20);
   x = i*4;
   output;
end;
run;

What It Does: This loop will try to perform 10 iterations, from i = 1 to 10, where the value in each row is equal to i multiplied by 4.

When It Stops: This loop will stop when the value of x exceeds 20 or when 10 iterations have been performed, whichever comes first.

3. DO UNTIL Loop

data data3;
x = 0;
do i = 1 to 10 until(x > 30);
   x = i*4;
   output;
end;
run;

What It Does: This loop will try to perform 10 iterations, from i = 1 to 10, where the value in each row is equal to i multiplied by 4.

When It Stops: This loop will stop when the value of x exceeds 30 or when 10 iterations have been performed, whichever comes first.

The following examples show how to use each DO loop in practice.

Example 1: DO Loop

We can use the following DO loop to create a dataset with 10 rows:

/*use DO loop to create dataset*/
data data1;
x = 0;
do i = 1 to 10;
   x = i*4;
   output;
end;
run;

/*view dataset*/
proc printdata=data1;

The result is a dataset that contains 10 rows where the values in column i range from 1 to 10 and the values in column x range from 4 to 40.

Note that you can use drop i to drop the index column from the dataset:

/*use DO loop to create dataset*/
data data1;
x = 0;
do i = 1 to 10;
   x = i*4;
   output;
end;
drop i;
run;

/*view dataset*/
proc printdata=data1;

Example 2: DO WHILE Loop

We can use the following DO WHILE  loop to create a dataset with a variable i from i = 1 to 10, where the value in each row is equal to i multiplied by 4 while x is less than 20:

/*use DO WHILE loop to create dataset*/
data data2;
x = 0;
do i = 1 to 10  while(x < 20);
   x = i*4;
   output;
end;
run;

/*view dataset*/
proc printdata=data2;

Notice that the loop stopped creating rows once x reached 20.

Example 3: DO UNTIL Loop

We can use the following DO UNTIL loop to create a dataset with a variable i from i = 1 to 10, where the value in each row is equal to i multiplied by 4 until x is greater than 30:

/*use DO UNTIL loop to create dataset*/
data data3;
x = 0;
do i = 1 to 10  until(x > 30);
   x = i*4;
   output;
end;
run;

/*view dataset*/
proc printdata=data3;

Notice that the loop stopped creating rows once x exceeded 30.

Additional Resources

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