Sample 24622: Drop variables from a SAS® data set whose values are all missing
The sample code on the Full Code tab illustrates how to drop variables from a SAS data set whose values are all missing.
The sample code uses arrays and iterative DO loops to determine whether a variable's values are missing for all observations. It then creates a macro variable whose value is the list of the variables to be dropped. The macro variable is used in a DROP statement in a subsequent DATA step.
These sample files and code examples are provided by SAS Institute
Inc. "as is" without warranty of any kind, either express or implied, including
but not limited to the implied warranties of merchantability and fitness for a
particular purpose. Recipients acknowledge and agree that SAS Institute shall
not be liable for any damages whatsoever arising out of their use of this material.
In addition, SAS Institute will provide no support for the materials contained herein.
The sample code below illustrates how to drop variables from a SAS data set whose values are all missing.
The sample code uses arrays and iterative DO loops to determine whether a variable's values are missing for all observations. It then creates a macro variable whose value is the list of the variables to be dropped. The macro variable is used in a DROP statement in a subsequent DATA step.
/* Create sample data set */
data missing;
input n1 n2 n3 n4 n5 n6 n7 n8 c1 $ c2 $ c3 $ c4 $;
datalines;
1 . 1 . 1 . 1 4 a . c .
1 1 . . 2 . . 5 e . g h
1 . 1 . 3 . . 6 . . k l
;
run;
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));
run;
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 in 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 that its 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';
end;
do i=1 to dim(char_vars);
if char_vars(i) ne '' then char_miss(i)='non-miss';
end;
/* 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)));
end;
do i= 1 to dim(char_vars);
if char_miss(i) = 'missing' then list=trim(list)||' '||trim(vname(char_vars(i)));
end;
call symput('mlist',list);
end;
run;
/* 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;
run;
proc print;
run;
These sample files and code examples are provided by SAS Institute
Inc. "as is" without warranty of any kind, either express or implied, including
but not limited to the implied warranties of merchantability and fitness for a
particular purpose. Recipients acknowledge and agree that SAS Institute shall
not be liable for any damages whatsoever arising out of their use of this material.
In addition, SAS Institute will provide no support for the materials contained herein.
Obs n1 n2 n3 n5 n7 n8 c1 c3 c4
1 1 . 1 1 1 4 a c
2 1 1 . 2 . 5 e g h
3 1 . 1 3 . 6 k l
Use arrays and iterative DO loops to determine whether a variable's values are missing for all observations. Create a macro variable whose value is the list of the variables to be dropped. Use the macro variable in a DROP statement in a subsequent DATA step.
| Type: | Sample |
| Topic: | SAS Reference ==> DATA Step
Data Management ==> Manipulation and Transformation ==> Array processing
|
| Date Modified: | 2009-08-07 10:27:04 |
| Date Created: | 2004-09-30 14:08:58 |
Operating System and Release Information
| SAS System | Base SAS | All | n/a | n/a |
