How can we do conditional iteration in a sas dataset

Question

How can we do iteration in a sas dataset. For example I have chosen the first. of a variable. And want to find the occurence of a particular condition and set a value when it satisfy

Answer 1

More information please... Possibly a concrete example

Answer 2

SAS data step has a built-in loop over observations. You don't have to do any thing, unless you want to, for some reason. For instance, the following generates a random number for each observation:

data one;
  set sashelp.class;
  rannum = ranuni(0);
run;

If you want to loop over variables, then there are arrays. For example, the following initializes variables, var1 to var10, with random numbers:

data one;
  array vars[1:10] var1-var10;
  do i = 1 to 10;
    vars[i] = ranuni(0);
  end;
run;

The first. and last. flags are automatically generated when you set a (sorted) data with a by statement. An example:

proc sort data=sashelp.class out=class;
  by age;
run;
data one;
  set class;
  by age;
  first = first.age;
  last = last.age;
run;
/* check */
proc print data=one;
run;
/* on lst
  Obs    Name       Age    first    last

  1    Joyce       11      1        0
  2    Thomas      11      0        1
  3    James       12      1        0
  4    Jane        12      0        0
  5    John        12      0        0
  6    Louise      12      0        0
  7    Robert      12      0        1
  8    Alice       13      1        0
  ...
 18    William     15      0        1
 19    Philip      16      1        1
*/