问下下段程序中如何确定以月份为粒度？




data q;
input a1 @@;
t=intnx('','1jan2008'd,_n_-1);
format t year4.;
cards;
0.039832315 -0.04981405 0.440898749 0.192210199 0.004092963 0.182916935 0.153680542 -0.020089853 0.029516383 0.316655953 0.863409983 -0.067150863 0.025617279 0.043785425 0.188884979 0.072928904 0.094813774 0.217219106 0.038215222 0.108607419 -0.069610067 0.212398751 0.676625068 0.022224068 0.118703399 -0.197133453 0.161988599 0.172801017 0.11149571 0.182710068 0.163322588 0.038467885 -0.034364501 0.240170592 0.764752427 -0.114312387 0.219943466 -0.245942781
;
run;
proc gplot data=q;
symbol i=spline v=star h=2 c=green;
plot a1*t;
run;