Here is one way. I combined the creation of a datetime variable and the transposition in the read step.
There are things to watch with the start stop of a days records so saving and restoring the values for the output may look odd.
Also I will leave it to you what you want to do about the interval between the last recorded temp and midnight. (Did you think that was an issue?).
Also this assumes that you have no missing records. If you do then there are things you need to address regarding the divisor to determine the interval step (hint: hours between current datetime and last date time with temp (less one) which requires modifying the transpose array code) and then number of steps in the do loop in the want datastep code.
If you do not have access to SAS/ETS you might need something like this.
data have;
informat TEMP_MAX TEMP_MIN TEMP0 TEMP3 TEMP6 TEMP9 TEMP12 TEMP15 TEMP18 TEMP21 best8. Date anydtdte.;
format date mmddyy10.;
input TEMP_MAX TEMP_MIN TEMP0 TEMP3 TEMP6 TEMP9 TEMP12 TEMP15 TEMP18 TEMP21 Date ;
array hr TEMP0 TEMP3 TEMP6 TEMP9 TEMP12 TEMP15 TEMP18 TEMP21;
do i=1 to dim(hr);
hour = (i-1)*3;
hrtemp= hr[i];
datetime= dhms(date,hour,0,0);
output;
end;
format datetime datetime.;
drop i TEMP0 TEMP3 TEMP6 TEMP9 TEMP12 TEMP15 TEMP18 TEMP21;
label hrtemp='Hourly Temp';
datalines;
32.00 23.00 27.00 25.00 23.00 26.10 32.00 30.00 28.00 28.00 1/1/2017
32.00 28.00 28.00 28.00 28.90 30.00 30.90 32.00 32.00 32.00 1/2/2017
32.00 3.00 32.00 32.00 25.00 14.00 12.00 10.90 6.10 3.00 1/3/2017
3.00 -5.10 1.00 -2.00 -5.10 -4.00 1.90 3.00 1.00 0.00 1/4/2017
;
run;
data want;
set have;
by date;
ldt = lag(datetime);
ltemp = lag(hrtemp);
savedt = datetime;
savetemp= hrtemp;
if first.date then output;
else do ;
int = (hrtemp - ltemp) / 3;
do i= 1 to 2;
datetime=intnx('hour',ldt,i);
hrtemp= round(ltemp + i*int,0.01);
output;
end;
datetime=savedt;
hrtemp=savetemp;
output;
end;
keep TEMP_MAX TEMP_MIN date datetime hrtemp;
run;
And you might want to thank SAS for providing the datetime data type and the functions associated with it. I had to write code in FORTRAN to do interpolation that crossed the 2000 century boundary and take into consideration of leap days and such.
