comparing dates and taking appropriate values if there is if not write -9999

Hi,

I was wondering if someone know how to deal with this topic.

I have to range of dates, one for instance the regular year and the second one, the same year but with some gaps and data going along with.
I am looking for a function that will take each date from the full year and searh for the same date in the range with a gaps and then take its coresponding vvalue if that date exists, if not it should write -9999.


i would really appreciate if someone can help me to resolve this since i have a lot of data like this.


thank you,