goptions reset=all; Title " "; Footnote " "; 
axis1 label=(font=swiss h=1.5 angle=90); 
*******************************************;

data last; input Y @@; 
date=intnx('month','01dec83'd,_n_);
format date monyy.;
cards; 
10 . . 12 18 40 . 13 18 . . . 10 . 10 10
  ;
proc print; 
proc expand data=last from=month to=month out=out1; 
  convert Y = ynew;  id date;
data out1; merge out1 last; 
by date; proc gplot data=out1; 
  plot Y*date Ynew*date /overlay;
  symbol1 v=dot i=none c=red; 
  symbol2 v=plus i=join c=black; 
title "Fill in missing Months"; run;  
proc expand data=last from=month to=week out=out2 outest=spline;  
  convert Y = Ywk; id date;
proc print data=out2(obs=5);  
proc print data=spline(obs=5); 
data out2; merge out2 last; 
by date; proc gplot data=out2;
  plot Y*date Ywk*date /overlay;
title "Convert to weekly data"; 
run;