Conditional merging

[Demographer]

Hello,

I have a dataset1 that looks like this :

NOIND	ALT	NO_DWEL	CHOICE	X1	X2
1	1	842	1	1	1
1	2	773	0	1	1
1	3	5543	0	1	1
2	1	76	1	0	1
2	2	6087	0	0	1
2	3	8228	0	0	1
3	1	737	1	1	0
3	2	7339	0	1	0
3	3	3006	0	1	0

And a dataset2 that looks like this:

NO_DWEL	X1	X2
1	1	0
2	0	0
3	1	1
4	1	0
…

I want to perform a conditional merging only when CHOICE=0, so the value of X1 and X2 of the dataset1 will be replaced by those of the dataset2 for lines when CHOICE=0 and will be keep as it is when CHOICE=1. The solution I find is probably not the best one and become complicated for further works… I rename variables of dataset2, perform a normal merge and then replace variables in the new dataset with IF THEN DO.

Can someone please help me to find a more efficient way to do this?

[Tom]

What are the BY variables for your merge? Is it just NO_DWEL?

[Tom · Accepted solution]

Add the variable CHOICE to DATASET2 and then include CHOICE in the BY statement for the MERGE.

data fix2 ; 
  set dataset2;
  choice=0;
run;

data want ;
  merge dataset1 (in=in1) fix2;
  by no_dwel choice;
  if in1;
run;