SAS use a lookup dataset like array in another dataset - dataset

Question

I have 1 data set with content description for a school
contents:
num description
content1 math
content2 spanish
content3 geography
content4 chemistry
content5 history
in another data set (students) i have the array content1-content5 and i use a flag to indicate content that have each student.
students
name age content1 content2 content3 content4 content5
BOB 15 1 1 1 1
BRYA 16
CARL 15 1 1
SUE 17 1 1 1
LOU 15 1
if i use a code like this:
data students1;
set students;
array content[5];
format allcontents $100.;
do i=1 to dim(content);
if content[i]=1 then do;
allcontents=cat(vname(content[i]),',',allcontents);
end;
end;
run;
the result is:
name age content1 content2 content3 content4 content5 allcontents
BOB 15 1 1 1 1 content1,content2,content3,content5,
BRYA 16
CARL 15 1 1 content2,content5,
SUE 17 1 1 1 content3,content4,content5,
LOU 15 1 content5
1) i want to use the name of the lookup table (data set contents) to use the name of the content and not the arrays names of content[1-5] in the variable allcontents. how can i do that?
2) and later i want the result by content description, not by student, like this:
description name age
math BOB 15
spanish BOB 15
geography BOB 15
history BOB 15
spanish CARL 15
history CARL 15
spanish SUE 17
chemistry SUE 17
history SUE 17
history LOU 15
is it possible?
thanks.

Answer 1

First, grab the %create_hash() macro from this post.
Use the hash table to look up the values.
data students1;
set students
array content[5];
format num $32. description $16.;
if _n_ = 1 then do;
%create_hash(cnt,num,description,"contents");
end;
do i=1 to 5;
if content[i]=1 then do;
num = vname(content[i]);
rc = cnt.find();
output;
end;
end;
keep description name age;
run;

Answer 2

I find proc transpose suitable. Doing once is enough for question 2) and twice for renaming the variables contents1-5 (hence question 1). The key is the ID statement in proc transpose which automatically rename variables by their corresponding transposed orders.
The code below should give you the desired answers (albeit the name are ordered alphabetically, which may not be the same as your original ordering).
/* original data sets */
data names;
input num $ description $;
cards;
content1 math
content2 spanish
content3 geography
content4 chemistry
content5 history
;run;
data students;
input name $ age content1 content2 content3 content4 content5;
cards;
BOB 15 1 1 1 . 1
BRYA 16 . . . . .
CARL 15 . 1 . . 1
SUE 17 . . 1 1 1
LOU 15 . . . . 1
;run;
/* transpose */
proc sort data=students out=tmp_sorted;
by name age;
run;
proc transpose data=tmp_sorted out=tmp_transposed;
by name age;
run;
/* merge the names of content1-5 */
* If you want to preserve ordering from contents1-contents5
* instead of alphabetical ordering of "description" column
* from a-z, do not drop the "num" column for further use.;
proc sql;
create table tmp_merged as
select B.description, A.name, A.age, B.num, A.COL1
from tmp_transposed as A
left join names as B
on A._NAME_=B.num
order by A.name, B.num;
quit;
/* transpose again */
proc transpose data=tmp_merged(drop=num) out=tmp_renamed(drop=_name_);
by name age;
ID description; *name the transposed variables;
run;
/* answer (1) */
data ans1;
set tmp_renamed;
array content[5] math--history;
format allcontents $100.;
do i=1 to dim(content);
* better use cats (cat does not seem to work);
if content[i]=1 then allcontents=cats(allcontents,',',vname(content[i]));
end;
*kill the leading comma;
allcontents=substr(allcontents,2,99);
run;
/* answer (2) */
data ans2(drop=num col1);
set tmp_merged;
where col1=1;
run;
*cleanup;
proc datasets lib=work nolist;
delete tmp_:;
quit;