Using a sas lookup table when the column number changes - sas

Question

I have two sas datasets,
Table 1 Table 2
col1 col2 col3 col4 col5 a b
. 1 2 3 4 1 1
1 5 8 6 1 1 4
2 5 9 7 1 4 3
3 6 9 7 1 2 1
4 6 9 7 2 2 2
where table 1 is a lookup table for values a and b in table 2, such that I can make a column c. In table 1 a is equivalent to col1 and b to row1 (i.e. the new column c in table 2 should read 5,1,7,5,9. How can I achieve this in sas. I was thinking of reading table 1 into a 2d array then get column c = array(a,b), but can't get it to work

Answer 1

Here's an IML solution, first, as I think this is really the 'best' solution for you - you're using a matrix, so use the matrix language. I'm not sure if there's a non-loop method - there may well be; if you want to find out, I would add the sas-iml tag to the question and see if Rick Wicklin happens by the question.
data table1;
input col1 col2 col3 col4 col5 ;
datalines;
. 1 2 3 4
1 5 8 6 1
2 5 9 7 1
3 6 9 7 1
4 6 9 7 2
;;;;
run;
data table2;
input a b;
datalines;
1 1
1 4
4 3
2 1
2 2
;;;;
run;
proc iml;
use table1;
read all var _ALL_ into table1[colname=varnames1];
use table2;
read all var _ALL_ into table2[colname=varnames2];
print table1;
print table2;
table3 = j(nrow(table2),3);
table3[,1:2] = table2;
do _i = 1 to nrow(table3);
table3[_i,3] = table1[table3[_i,1]+1,table3[_i,2]+1];
end;
print table3;
quit;

Answer 2

Here is the temporary array solution. It's not all that pretty. If speed is an issue you don't have to loop over the array to insert it, you can use direct memory access, but I don't want to do that unless speed is a huge issue (and if it is, you should use a better data structure first).
data table3;
set table2;
array _table1[4,4] _temporary_;
if _n_ = 1 then do;
do _i = 1 by 1 until (eof);
set table1(firstobs=2) nobs=_nrows end=eof;
array _cols col2-col5;
do _j = 1 to dim(_cols);
_table1[_i,_j] = _cols[_j];
end;
end;
end;
c = _table1[a,b];
keep a b c;
run;

Answer 3

Just use the POINT= option on a SET statement to pick the row. You can then use an ARRAY to pick the column.
data table1 ;
input col1-col4 ;
cards;
5 8 6 1
5 9 7 1
6 9 7 1
6 9 7 2
;
data table2 ;
input a b ;
cards;
1 1
1 4
4 3
2 1
2 2
;
data want ;
set table2 ;
p=a ;
set table1 point=p ;
array col col1-col4 ;
c=col(b);
drop col1-col4;
run;