Hello.

I have a dataset with multiple follow-up dates (fu1, fu2 etc.) and corresponding morbidity scores (morb_a1, morb_b1, morb_a2, morb_b2 etc).

I seek to identify the follow-up dates closest to certain time points after start of radiotherapy (RTstart) and very importantly their corresponding morbidity scores. The time points are 3, 6, 12, 24, 36, 48 and 60 months.
If the follow-up date closest to this time point has a missing value for its corresponding morbidity, I wish to identify the second-nearet follow-up date and its corresponding morbidity score and so forth.
The format of my follow-up dates are %tdnn/dd/CCYY.

id RTstart fu1 morb_a1 morb_b1 fu2 morb_a2 morb_b2 fu3 morb_a3 morb_b3


Thanks a lot in advance,

Line.