flagging an observation

[pmpradhan]

My data looks like below without the flag, I want to create a flag that has the value of 1 when B> A (0 when reverse is true)and it should be missing when either A or B has a missing value.

A	B	Flag
.	65	.
.	12	.
626	5	0
20	.	.
.	23	.
10	25	1

I have tried this;

data X;
set Y;
if (A ne .) or (B ne .) and B >A then flag=1;

else flag=0;
run;

and didn't work. 

Please help!

[pmpradhan · Accepted solution]

data x;
set y;
if A =. then flag=.;
else if B=. then flag=.;
else if B>A then flag=1;
else if A >B then flag=0;
run;
Coding for each condition gave me result!

[novinosrin]

data want;
set have;
if nmiss(a,b)=0 then flag=b>a;
run;

EDIT: I really appreciate you self attempt and effort to get a working code. However, once you throw  open a thread in the community, you are sure to get some robust solutions. But well done mate!