An end-of-file condition occurs when you try to read past the end of a data set or when you point to an observation that exceeds the number of observations in a data set. If an end-of-file condition occurs inside a DO DATA iteration loop, control passes to the first statement after the DO DATA loop.

The following example uses a DO DATA loop to read observations from the Sashelp.Class data set. The loop reads the data one observation at a time and accumulates the weights of the students in the SAS/IML matrix named sum. After the data are read, the variable sum contains the sum of the weights for the class.

proc iml;
use Sashelp.Class;
/* if data set already open, use   
   setin class point 0; */
sum=0;
do data;
   read next var{weight};
   sum = sum + weight;
end;
print sum;

The example shows how to read data one observation at a time within a DO loop. However, there are more efficient ways to read data in the SAS/IML language. If all the data can fit into memory, it is more efficient to read all the data into a vector and use vector operations to compute statistical quantities such as a sum. For example, the following statements compute the same quantity (the sum of the Weight variable) but are more efficient:

read all var{weight};
sum = sum(weight);