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Date:         Thu, 9 Nov 2006 11:48:31 -0800
Reply-To:     shiling99@YAHOO.COM
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         shiling99@YAHOO.COM
Subject:      Re: find and drop empty variables
Comments: To:
In-Reply-To:  <>
Content-Type: text/plain; charset="us-ascii"

The probility for a USUAL variable with all missing values is very small. I think it is a good way to select a small sample from your LARGE data set (gigbytes). You can quickly find out a small list of variables with all missing value in your sample data. Then proc freq, proc mean against whole data set for these variables ONLY. This will save you a lot of time when you work on LARGE data set. Attached below is a sample pgm to illustrate the idea and you may modify for your work.


data t1; array nv(*) n1-n30; na=.; array cv(*) $ c1-c30; ca=' '; do i = 1 to 1000000; do j=1 to dim(nv); nv(j)=rannor(123); end; do j=1 to dim(cv); cv(j)=compress(put(rannor(123),3.)); if cv(j)='0' then cv(j)=' '; end; output; end; keep n: c:; run;

proc format library=work; invalue _c ' '=. other=1; run;

proc sql ; select '_'||trim(name)||'=input('||trim(name)||',_c.)' into : cvarlist separated by ';' from sashelp.vcolumn where libname='WORK' and memname='T1' and type='char' ; quit;

data t1v/view=t1v; do i=1 to nobs by 1000; set t1 point=i nobs=nobs; &cvarlist ; output; end; stop; ; run;

proc means data=t1v noprint; var _numeric_; output out=varlist(drop=_freq_ _type_) n=; run;

data _null_; set varlist; array allv(*) _numeric_; do i = 1 to dim(allv); vname=vname(allv(i)); if substr(vname,1,1)='_' then vname=substr(vname,2); if allv(i)=0 then put 'var with all missing value in 1/1000 sample --->' vname; end; run;

Alexander Norderwind wrote: > I have the problem that a big database I import to SAS with proc sql and > ODBC has about thousand variables (fields) and lots of them are empty all over. > Thus I would like dropping them to get rid of this ballast. > Therefore I first have to find out, which of them really are empty. > Does anybody have a suggestion how to solve my problem? > Would be nice! > Xander

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