Processing a Limited Number of Observations

First and Last Observations

Use FIRSTOBS= n to cause processing to begin at the nth observation.
Use OBS= n to cause processing to stop at the nth observation.

Can assign first and last observations via:

Data set options in the SET statement

        set test(firstobs= 300); 
        set test(obs= 500); 
        set test(firstobs= 25 obs= 325);

Data set options in Procedures

        proc print data= test(firstobs= 5);
        proc print data= test(obs= 50); 
        proc print data= test(firstobs= 5 obs= 100);

System options

        options firstobs= 10; 
        options obs= 200; 
        options firstobs= 15 obs= 75;

The _N_ Variable

Automatic variable that is initially set to 1 at the start of the data step.
Increments by 1 after each loop of the data step.

Can use _n_ to specify number of observations to process in your data step.

  data new;
   set in.test;
   *** Select the first 500 observations using the _N_ Variable ***;        
   if _n_ <= 500;
 
 run;

Using the WHERE statement with the OBS= option

Using the WHERE statement in conjunction with the OBS= option first selects the observations with the WHERE condition and then only prints up to the first 40 observations of when that condition is true.
```
   proc print data= new(obs= 40);
     where gender = 2;
   run;
```

Random Sample

Look at a random sample of the data using the RANUNI function.

The following is an example of an approximate-sized random sample without replacement:

   proc print data= ag (obs= 30);
     id VILL94 LEKTI94;
     var TRACTOR LANDOWNED PLOTS RICE CASSAVA SUGAR;
     where ranuni(333) <= 0.10;
   run;

The seed or arbitrary starting point (333 above) should be nonnegative.
You can reproduce a random sample by using the same seed.
If you choose a seed of zero, the computer clock time is used at execution.

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