Create SAS data set conditionally on other data sets - sas

Question

I have 6 identical SAS data sets. They only differ in terms of the values of the observations.
How can I create one output data, which finds the maximum value across all the 6 data sets for each cell?
The update statement seems a good candidate, but it cannot set a condition.
data1
v1 v2 v3
1 1 1
1 2 3
data2
v1 v2 v3
1 2 3
1 1 1
Result
v1 v2 v3
1 2 3
1 2 3

Answer 1

If need be the following could be automated by "PUT" statements or variable arrays.
***ASSUMES DATA SETS ARE SORTED BY ID;
Data test;
do until(last.id);
set a b c;
by id;
if v1 > updv1 then updv1 = v1;
if v2 > updv2 then updv2 = v2;
if v3 > updv3 then updv3 = v3;
end;
drop v1-v3;
rename updv1-updv3 = v1-v3;
run;
To provide a more complete solution to Rico's question(assuming 6 datasets e.g. d1-d6) one could do it this way:
Data test;
array v(*) v1-v3;
array updv(*) updv1-updv3;
do until(last.id);
set d1-d6;
by id;
do i = 1 to dim(v);
if v(i) > updv(i) then updv(i) = v(i);
end;
end;
drop v1-v3;
rename updv1-updv3 = v1-v3;
run;
proc print;
var id v1-v3;
run;

Answer 2

See below. For a SAS beginner might be too complex. I hope the comments do explain it a bit.
/* macro rename_cols_opt to generate cols_opt&n variables
- cols_opt&n contains generated code for dataset RENAME option for a given (&n) dataset
*/
%macro rename_cols_opt(n);
%global cols_opt&n max&n;
proc sql noprint;
select catt(name, '=', name, "&n") into: cols_opt&n separated by ' '
from dictionary.columns
where libname='WORK' and memname='DATA1'
and upcase(name) ne 'MY_ID_COLUMN'
;
quit;
%mend;
/* prepare macro variables = pre-generate the code */
%rename_cols_opt(1)
%rename_cols_opt(2)
%rename_cols_opt(3)
%rename_cols_opt(4)
%rename_cols_opt(5)
%rename_cols_opt(6)
/* create macro variable keep_list containing names of output variables to keep (based on DATA1 structure, the code expects those variables in other tables as well */
proc sql noprint;
select trim(name) into: keep_list separated by ' '
from dictionary.columns
where libname='WORK' and memname='DATA1'
;
quit;
%put &keep_list;
/* macro variable maxcode contains generated code for calculating all MAX values */
proc sql noprint;
select cat(trim(name), ' = max(of ', trim(name), ":)") into: maxcode separated by '; '
from dictionary.columns
where libname='WORK' and memname='DATA1'
and upcase(name) ne 'MY_ID_COLUMN'
;
quit;
%put "&maxcode";
data result1 / view =result1;
merge
data1 (in=a rename=(&cols_opt1))
data2 (in=b rename=(&cols_opt2))
data3 (in=b rename=(&cols_opt3))
data4 (in=b rename=(&cols_opt4))
data5 (in=b rename=(&cols_opt5))
data6 (in=b rename=(&cols_opt6))
;
by MY_ID_COLUMN;
&maxcode;
keep &keep_list;
run;
/* created a datastep view, now "describing" it to see the generated code */
data view=result1;
describe;
run;

Answer 3

Here's another attempt that is scalable against any number of datasets and variables. I've added in an ID variable this time as well. Like the answer from #vasja, there are some advanced techniques used here. The 2 solutions are in fact very similar, I've used 'call execute' instead of a macro to create the view. My solution also requires the dataset names to be stored in a dataset.
/* create dataset of required dataset names */
data datasets;
input ds_name $;
cards;
data1
data2
;
run;
/* dummy data */
data data1;
input id v1 v2 v3;
cards;
10 1 1 1
20 1 2 3
;
run;
data data2;
input id v1 v2 v3;
cards;
10 1 2 3
20 1 1 1
;
run;
/* create dataset, macro list and count of variables names */
proc sql noprint;
create table variables as
select name as v_name from dictionary.columns
where libname='WORK' and upcase(memname)='DATA1' and upcase(name) ne 'ID';
select name, count(*) into :keepvar separated by ' ',
:numvar
from dictionary.columns
where libname='WORK' and upcase(memname)='DATA1' and upcase(name) ne 'ID';
quit;
/* create view that joins all datasets, renames variables and calculates maximum value per id */
data _null_;
set datasets end=last;
if _n_=1 then call execute('data data_all / view=data_all; merge');
call execute (trim(ds_name)|| '(rename=(');
do i=1 to &numvar.;
set variables point=i;
call execute(trim(v_name)||'='||catx('_',v_name,_n_));
end;
call execute('))');
if last then do;
call execute('; by id;');
do i=1 to &numvar.;
set variables point=i;
call execute(trim(v_name)||'='||'max(of '||trim(v_name)||':);');
end;
call execute('run;');
end;
run;
/* create dataset of maximum values per id per variable */
data result (keep=id &keepvar.);
set data_all;
run;