check difference of PROC SUMMARY <> PROC MEANS (not finished)

***  if VAR is missing, sas will drop that records when calculating mean. To include that records, we can impute that missing var by 0 ***;

data test;
  input a $ 1-3 b 4-5 ;
  cards;
  a 1
  a
  a 3
  b
  b 2
  b 1
  c 1
  c
    1
    4
  ;
run;

proc print data=test noobs;
  title "print of original data";
run;

proc summary data=test nway missing;
  var b;
  class a;
  output out=sum1(drop=_type_ _freq_) mean=;
run;

proc print data=sum1;
  title "Summary with MISSING opinion";
run;

proc summary data=test nway;
  var b;
  class a;
  output out=sum2(drop=_type_ _freq_) mean=;
run;

proc print data=sum2;
  title "Summary without MISSING opinion";
run;

proc means data=test nway missing;
  var b;
  class a;
  output out=means1(drop=_type_ _freq_) mean=;
run;

proc print data=means1;
  title "Means with MISSING opinion";
run;

proc summary data=test nway;
  var b;
  class a;
  output out=means2(drop=_type_ _freq_) mean=;
run;

proc print data=means2;
  title "Means without MISSING opinion";
run;

^LSummary with MISSING opinion

Obs    a     b

 1          2.5
 2     a    2.0
 3     b    1.5
 4     c    1.0


^LSummary without MISSING opinion

Obs    a     b

 1     a    2.0
 2     b    1.5
 3     c    1.0


^LMeans with MISSING opinion

Obs    a     b

 1          2.5
 2     a    2.0
 3     b    1.5
 4     c    1.0


^LMeans without MISSING opinion

Obs    a     b

 1     a    2.0
 2     b    1.5
 3     c    1.0