Here are two different ways to replace values in an existing table

• overwriting the entire table with a new copy of itself
  • data name; set name; …
• modifying values in-place within existing table
  • data name; modify name; …

Example

1    data class;
2      set sashelp.class;
3    run;

NOTE: There were 19 observations read from the data set SASHELP.CLASS.
NOTE: The data set WORK.CLASS has 19 observations and 5 variables.
NOTE: DATA statement used (Total process time):
      real time           0.17 seconds
      cpu time            0.00 seconds


4
5    data class;     /* output data set named is same as input data set */
6      set class;
7      age = age * 2;
8    run;

NOTE: There were 19 observations read from the data set WORK.CLASS.
NOTE: The data set WORK.CLASS has 19 observations and 5 variables.
NOTE: DATA statement used (Total process time):
      real time           0.01 seconds
      cpu time            0.03 seconds


9
10   data class;      /* output data set name */
11     modify class;  /* is same as modify name, values updated in place */  
12     age = age / 2;
13   run;             /* observations are rewritten (see log) */

NOTE: There were 19 observations read from the data set WORK.CLASS.
NOTE: The data set WORK.CLASS has been updated.  There were 19 observations rewritten, 0
      observations added and 0 observations deleted.
NOTE: DATA statement used (Total process time):
      real time           0.05 seconds
      cpu time            0.00 seconds

A third way would be to use SQL UPDATE statement with sets based on coalesce, however, that is not amenable to array processing.

Proc SQL;
  update mydata set 
    a1 = coalesce (a1,0)
  , s2 = coalesce (a2,0)
  … 
  ;