How do I conditionally select variables in PROC SQL? - sas

Question

I have calculated a frequency table in a previous step. Excerpt below:
I want to automatically drop all variables from this table where the frequency is missing. In the excerpt above, that would mean the variables "Exkl_UtgUtl_Taxi_kvot" and "Exkl_UtgUtl_Driv_kvot" would need to be dropped.
I try the following step in PROC SQL (which ideally I will repeat for all variables in the table):
PROC SQL;
CREATE TABLE test3 as
SELECT (CASE WHEN Exkl_UtgUtl_Flyg_kvot!=. THEN Exkl_UtgUtl_Flyg_kvot ELSE NULL END)
FROM stickprovsstorlekar;
quit;
This fails, however, since SAS does not like NULL values. How do I do this?
I tried just writing:
PROC SQL;
CREATE TABLE test3 as
SELECT (CASE WHEN Exkl_UtgUtl_Flyg_kvot!=. THEN Exkl_UtgUtl_Flyg_kvot)
FROM stickprovsstorlekar;
quit;
But that just generates a variable with an automatically generated name (like DATA_007). I want all variables containing missing values to be totally excluded from the results.

Answer 1

Let's say you have 10 variables, where var1, var3, var5, var7, and var9 have missing values in the first observation. We want to select only the variables with no missing observations.
var1 var2 var3 var4 var5 var6 var7 var8 var9 var10
. 8 . 9 . 6 . 1 . 4
5 1 2 7 2 7 2 9 7 7
5 9 7 7 6 8 5 6 4 9
...
First, let's find all variables that have missing observations:
proc means data=have noprint;
var _NUMERIC_;
output out=missing nmiss=;
run;
Then transpose this output table so it's easier to work with:
proc transpose data=missing out=missing_tpose;
run;
We now have a table that looks like this:
_NAME_ COL1
_TYPE_ 0
_FREQ_ 10
var1 1
var2 0
var3 1
var4 0
var5 1
var6 0
var7 1
var8 0
var9 1
var10 0
When COL1 is > 0 and the name is not _TYPE_ or _FREQ_, that means the variable has missing values. Let's extract the name of the variable from _NAME_ into a comma-separated list.
proc sql noprint;
select _NAME_
into :vars separated by ','
from missing_tpose
where COL1 = 0 AND _NAME_ NOT IN('_TYPE_', '_FREQ_')
;
quit;
%put &vars and you'll see all of the non-missing values that can be passed into SQL.
var2,var4,var6,var8,var10
Now we have a dynamic way to select variables with only non-missing values.
proc sql;
create table want as
select &vars
from have
;
quit;