Mar 21, 2012

Drop variables from a SAS data set when all its values are missing...

Drop variables from a SAS data set when all its values are missing…
/* Create sample data set */
data missing;
  input n1 n2 n3 n4 n5 n6 n7 n8 c1 $ c2 $ c3 $ c4 $;
1 . 1 . 1 . 1 4 a . c .
1 1 . . 2 . . 5 e . g h
1 . 1 . 3 . . 6 . . k l
options symbolgen;
/*Create two macro variables, num_qty and char_qty, to hold*/
/*the number of numeric and character variables, respectively.*/
/*These will be used to define the number of elements in the ARRAYs*/
/*in the next DATA step.*/
data _null_;
  set missing (obs=1);
  array num_vars[*] _NUMERIC_;
  array char_vars[*] _CHARACTER_;
  call symputx('num_qty', dim(num_vars));
  call symputx('char_qty', dim(char_vars));
data _null_;
  set missing end=finished;
  /* Use the reserved word _NUMERIC_ to load all numeric variables  */
  /* into the NUM_VARS array.  Use the reserved word _CHARACTER_ to */
  /* to load all character variables into the CHAR_VARS array.      */
  array num_vars[*] _NUMERIC_;
  array char_vars[*] _CHARACTER_;
  /* Create 'flag' arrays for the variables in NUM_VARS and CHAR_VARS. */
  /* Initialize their values to 'missing'.  Values initialized on an   */
  /* array statement are retained.                                     */
  array num_miss [&num_qty] $ (&num_qty * 'missing');
  array char_miss [&char_qty] $ (&char_qty * 'missing');
  /* LIST will contain the list of variables to be dropped.  Ensure  */
  /* it's length is sufficient.                                      */
  length list $ 50;
  /* Check for non-missing values.  Reassign the corresponding 'flag' */
  /* value accordingly.                                               */
  do i=1 to dim(num_vars);
    if num_vars(i) ne . then num_miss(i)='non-miss';
  do i=1 to dim(char_vars);
    if char_vars(i) ne '' then char_miss(i)='non-miss';
  /* On the last observation of the data set, if a 'flag' value is still */
  /* 'missing', the variable needs to be dropped.  Concatenate the       */
  /* variable's name onto LIST to build the values of a DROP statement   */
  /* to be executed in another step.                                     */
  if finished then do;
  do i= 1 to dim(num_vars);
    if num_miss(i) = 'missing' then list=trim(list)||' '||trim(vname(num_vars(i)));
  do i= 1 to dim(char_vars);
    if char_miss(i) = 'missing' then list=trim(list)||' '||trim(vname(char_vars(i)));
  call symput('mlist',list);
/* Use the macro variable MLIST in the DROP statement.  PROC DATASETS can */
/* be used to drop the variables instead of a DATA step.                  */
data notmiss;
  set missing;
  drop &mlist;
proc print;