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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