Hi there, I am trying to do the same thing as this user -- do a linear interpolation.  However my data are semi-annual and I want to go to a monthly frequency.  I have three reported periods: Dec. 2014, June 2015 and Dec. 2015 with the remaining months in between to be generated.  I have attached a screenshot of the data.       I tried modifying code in this thread but no luck.     I am new to this so any help greatly appreciated.   Thanks Jack ... View more

I know you got many answers. I just tried it and got a simpler solution. data h1; input port $ year qtr stock  $ amount; cards; p1 2000 1 s1 100 p1 2000 1 s2 200 p1 2000 1 s3  50 p1 2000 1 s4 100 p1 2000 2 s1 150 p1 2000 2 s3 100 p1 2000 2 s4 100 p1 2000 3 s1 200 p1 2000 3 s3 100 p1 2000 3 s4 150 p1 2000 3 s5 100 ; run; data h2(keep = stock amount_1); set h1; if qtr=1; rename amount=amount_1; run; proc sort data=h1;by stock;run; proc sort data=h2;by stock;run; data h3; merge h1(in=a) h2(in=b); by stock; if a; final_amt=amount-amount_1; run; Hope this helps ! ... View more

Thank you Reeza! Yes, I can now see that it was creating the trouble. I learned one lessen today ... View more