How to recode values of a variable based on the maxmium value in the variable, for hundreds of variables? - sas

Question

I want to recode the max value of a variable as 1 and 0 when it is not. For each variable, there may be multiple observations with the max value. The max value for each value is not fixed, i.e. from cycle to cycle the max value for each variable may change. And there are hundreds of variables, cannot "hard-code" anything.
The final product would have the same dimensions as the original table, i.e. equal number of rows and columns as a matrix of 0s and 1s.
This is within SAS. I attempted to calculate the max of each variable and then append these max as a new observation into the data. Then comparing down the column of each variable against the "max" observation... looking into examples of the following did not help:
SQL
Array in datastep
proc transpose
formatting
Any insight would be much appreciated.

Answer 1

Here is a version done with SQL:
The idea is that we first calculate the maximum. The Latter select. Then we join the data to original and the outer the case-select specifies if the flag is set up or not.
data begin;
input var value;
cards;
1 1
1 2
1 3
1 2.5
1 1.7
1 3
2 34
2 33
2 33
2 33.7
2 34
2 34
; run;
proc sql;
create table result as
select a.var, a.value, case when a.value = b.maximum then 1 else 0 end as is_max from
(select * from begin) a
left join
(select max(value) as maximum, var from begin group by var) b
on a.var = b.var
;
quit;

Answer 2

To avoid "hard-code" you need to use some code generation.
First let's figure out what code you could use to solve the problem. Later we can look into ways to generate that code.
It is probably easiest to do this with PROC SQL code. SAS will allow you to reference the MAX() value of a variable. Also note that SAS evaluates boolean expressions to 1 (TRUE) or 0 (FALSE). So you just want to generate code like:
proc sql;
create table want as
select var1=max(var1) as var1
, var2=max(var2) as var2
from have
;
quit;
To generate the code you need a list of the variables in your source dataset. You can get those with PROC CONTENTS but also with the metadata table (view) DICTIONARY.COLUMNS (also accessible as SASHELP.VCOLUMN from outside PROC SQL).
If the list of variables is small then you could generate the code into a single macro variable.
proc sql noprint;
select catx(' ',cats(name,'=max(',name,')'),'as',name)
into :varlist separated by ','
from dictionary.columns
where libname='WORK' and memname='HAVE'
order by varnum
;
create table want as
select &varlist
from have
;
quit;
The maximum number of characters that will fit into a macro variable is 64K. So long enough for about 2,000 variables with names of 8 characters each.
Here is little more complex way that uses PROC SUMMARY and a data step with a temporary array. It does not really need any code generation.
%let dsin=sashelp.class(obs=10);
%let dsout=want;
%let varlist=_numeric_;
proc summary data=&dsin nway ;
var &varlist;
output out=summary(drop=_type_ _freq_) max= ;
run;
data &dsout;
if 0 then set &dsin;
array vars &varlist;
array max [10000] _temporary_;
if _n_=1 then do;
set summary ;
do _n_=1 to dim(vars);
max[_n_]=vars[_n_];
end;
end;
set &dsin;
do _n_=1 to dim(vars);
vars[_n_]=vars[_n_]=max[_n_];
end;
run;
Results:
Obs Name Sex Age Height Weight
1 Alfred M 0 1 1
2 Alice F 0 0 0
3 Barbara F 0 0 0
4 Carol F 0 0 0
5 Henry M 0 0 0
6 James M 0 0 0
7 Jane F 0 0 0
8 Janet F 1 0 1
9 Jeffrey M 0 0 0
10 John M 0 0 0